src/HOL/Transcendental.thy
 author hoelzl Mon Mar 17 19:12:52 2014 +0100 (2014-03-17) changeset 56181 2aa0b19e74f3 parent 56167 ac8098b0e458 child 56193 c726ecfb22b6 permissions -rw-r--r--
unify syntax for has_derivative and differentiable
```     1 (*  Title:      HOL/Transcendental.thy
```
```     2     Author:     Jacques D. Fleuriot, University of Cambridge, University of Edinburgh
```
```     3     Author:     Lawrence C Paulson
```
```     4     Author:     Jeremy Avigad
```
```     5 *)
```
```     6
```
```     7 header{*Power Series, Transcendental Functions etc.*}
```
```     8
```
```     9 theory Transcendental
```
```    10 imports Fact Series Deriv NthRoot
```
```    11 begin
```
```    12
```
```    13 subsection {* Properties of Power Series *}
```
```    14
```
```    15 lemma lemma_realpow_diff:
```
```    16   fixes y :: "'a::monoid_mult"
```
```    17   shows "p \<le> n \<Longrightarrow> y ^ (Suc n - p) = (y ^ (n - p)) * y"
```
```    18 proof -
```
```    19   assume "p \<le> n"
```
```    20   hence "Suc n - p = Suc (n - p)" by (rule Suc_diff_le)
```
```    21   thus ?thesis by (simp add: power_commutes)
```
```    22 qed
```
```    23
```
```    24 lemma lemma_realpow_diff_sumr:
```
```    25   fixes y :: "'a::{comm_semiring_0,monoid_mult}"
```
```    26   shows
```
```    27     "(\<Sum>p=0..<Suc n. (x ^ p) * y ^ (Suc n - p)) =
```
```    28       y * (\<Sum>p=0..<Suc n. (x ^ p) * y ^ (n - p))"
```
```    29   by (simp add: setsum_right_distrib lemma_realpow_diff mult_ac del: setsum_op_ivl_Suc)
```
```    30
```
```    31 lemma lemma_realpow_diff_sumr2:
```
```    32   fixes y :: "'a::{comm_ring,monoid_mult}"
```
```    33   shows
```
```    34     "x ^ (Suc n) - y ^ (Suc n) =
```
```    35       (x - y) * (\<Sum>p=0..<Suc n. (x ^ p) * y ^ (n - p))"
```
```    36 proof (induct n)
```
```    37   case 0 show ?case
```
```    38     by simp
```
```    39 next
```
```    40   case (Suc n)
```
```    41   have "x ^ Suc (Suc n) - y ^ Suc (Suc n) = x * (x * x ^ n) - y * (y * y ^ n)"
```
```    42     by simp
```
```    43   also have "... = y * (x ^ (Suc n) - y ^ (Suc n)) + (x - y) * (x * x ^ n)"
```
```    44     by (simp add: algebra_simps)
```
```    45   also have "... = y * ((x - y) * (\<Sum>p=0..<Suc n. (x ^ p) * y ^ (n - p))) + (x - y) * (x * x ^ n)"
```
```    46     by (simp only: Suc)
```
```    47   also have "... = (x - y) * (y * (\<Sum>p=0..<Suc n. (x ^ p) * y ^ (n - p))) + (x - y) * (x * x ^ n)"
```
```    48     by (simp only: mult_left_commute)
```
```    49   also have "... = (x - y) * (\<Sum>p = 0..<Suc (Suc n). x ^ p * y ^ (Suc n - p))"
```
```    50     by (simp add: setsum_op_ivl_Suc [where n = "Suc n"] distrib_left lemma_realpow_diff_sumr
```
```    51              del: setsum_op_ivl_Suc)
```
```    52   finally show ?case .
```
```    53 qed
```
```    54
```
```    55 corollary power_diff_sumr2: --{* @{text COMPLEX_POLYFUN} in HOL Light *}
```
```    56   fixes x :: "'a::{comm_ring,monoid_mult}"
```
```    57   shows   "x^n - y^n = (x - y) * (\<Sum>i=0..<n. y^(n - Suc i) * x^i)"
```
```    58 using lemma_realpow_diff_sumr2[of x "n - 1" y]
```
```    59 by (cases "n = 0") (simp_all add: field_simps)
```
```    60
```
```    61 lemma lemma_realpow_rev_sumr:
```
```    62    "(\<Sum>p=0..<Suc n. (x ^ p) * (y ^ (n - p))) =
```
```    63     (\<Sum>p=0..<Suc n. (x ^ (n - p)) * (y ^ p))"
```
```    64   apply (rule setsum_reindex_cong [where f="\<lambda>i. n - i"])
```
```    65   apply (rule inj_onI, auto)
```
```    66   apply (metis atLeastLessThan_iff diff_diff_cancel diff_less_Suc imageI le0 less_Suc_eq_le)
```
```    67   done
```
```    68
```
```    69 lemma power_diff_1_eq:
```
```    70   fixes x :: "'a::{comm_ring,monoid_mult}"
```
```    71   shows "n \<noteq> 0 \<Longrightarrow> x^n - 1 = (x - 1) * (\<Sum>i=0..<n. (x^i))"
```
```    72 using lemma_realpow_diff_sumr2 [of x _ 1]
```
```    73   by (cases n) auto
```
```    74
```
```    75 lemma one_diff_power_eq':
```
```    76   fixes x :: "'a::{comm_ring,monoid_mult}"
```
```    77   shows "n \<noteq> 0 \<Longrightarrow> 1 - x^n = (1 - x) * (\<Sum>i=0..<n. x^(n - Suc i))"
```
```    78 using lemma_realpow_diff_sumr2 [of 1 _ x]
```
```    79   by (cases n) auto
```
```    80
```
```    81 lemma one_diff_power_eq:
```
```    82   fixes x :: "'a::{comm_ring,monoid_mult}"
```
```    83   shows "n \<noteq> 0 \<Longrightarrow> 1 - x^n = (1 - x) * (\<Sum>i=0..<n. x^i)"
```
```    84 by (metis one_diff_power_eq' [of n x] nat_diff_setsum_reindex)
```
```    85
```
```    86 text{*Power series has a `circle` of convergence, i.e. if it sums for @{term
```
```    87   x}, then it sums absolutely for @{term z} with @{term "\<bar>z\<bar> < \<bar>x\<bar>"}.*}
```
```    88
```
```    89 lemma powser_insidea:
```
```    90   fixes x z :: "'a::real_normed_div_algebra"
```
```    91   assumes 1: "summable (\<lambda>n. f n * x ^ n)"
```
```    92     and 2: "norm z < norm x"
```
```    93   shows "summable (\<lambda>n. norm (f n * z ^ n))"
```
```    94 proof -
```
```    95   from 2 have x_neq_0: "x \<noteq> 0" by clarsimp
```
```    96   from 1 have "(\<lambda>n. f n * x ^ n) ----> 0"
```
```    97     by (rule summable_LIMSEQ_zero)
```
```    98   hence "convergent (\<lambda>n. f n * x ^ n)"
```
```    99     by (rule convergentI)
```
```   100   hence "Cauchy (\<lambda>n. f n * x ^ n)"
```
```   101     by (rule convergent_Cauchy)
```
```   102   hence "Bseq (\<lambda>n. f n * x ^ n)"
```
```   103     by (rule Cauchy_Bseq)
```
```   104   then obtain K where 3: "0 < K" and 4: "\<forall>n. norm (f n * x ^ n) \<le> K"
```
```   105     by (simp add: Bseq_def, safe)
```
```   106   have "\<exists>N. \<forall>n\<ge>N. norm (norm (f n * z ^ n)) \<le>
```
```   107                    K * norm (z ^ n) * inverse (norm (x ^ n))"
```
```   108   proof (intro exI allI impI)
```
```   109     fix n::nat
```
```   110     assume "0 \<le> n"
```
```   111     have "norm (norm (f n * z ^ n)) * norm (x ^ n) =
```
```   112           norm (f n * x ^ n) * norm (z ^ n)"
```
```   113       by (simp add: norm_mult abs_mult)
```
```   114     also have "\<dots> \<le> K * norm (z ^ n)"
```
```   115       by (simp only: mult_right_mono 4 norm_ge_zero)
```
```   116     also have "\<dots> = K * norm (z ^ n) * (inverse (norm (x ^ n)) * norm (x ^ n))"
```
```   117       by (simp add: x_neq_0)
```
```   118     also have "\<dots> = K * norm (z ^ n) * inverse (norm (x ^ n)) * norm (x ^ n)"
```
```   119       by (simp only: mult_assoc)
```
```   120     finally show "norm (norm (f n * z ^ n)) \<le>
```
```   121                   K * norm (z ^ n) * inverse (norm (x ^ n))"
```
```   122       by (simp add: mult_le_cancel_right x_neq_0)
```
```   123   qed
```
```   124   moreover have "summable (\<lambda>n. K * norm (z ^ n) * inverse (norm (x ^ n)))"
```
```   125   proof -
```
```   126     from 2 have "norm (norm (z * inverse x)) < 1"
```
```   127       using x_neq_0
```
```   128       by (simp add: norm_mult nonzero_norm_inverse divide_inverse [where 'a=real, symmetric])
```
```   129     hence "summable (\<lambda>n. norm (z * inverse x) ^ n)"
```
```   130       by (rule summable_geometric)
```
```   131     hence "summable (\<lambda>n. K * norm (z * inverse x) ^ n)"
```
```   132       by (rule summable_mult)
```
```   133     thus "summable (\<lambda>n. K * norm (z ^ n) * inverse (norm (x ^ n)))"
```
```   134       using x_neq_0
```
```   135       by (simp add: norm_mult nonzero_norm_inverse power_mult_distrib
```
```   136                     power_inverse norm_power mult_assoc)
```
```   137   qed
```
```   138   ultimately show "summable (\<lambda>n. norm (f n * z ^ n))"
```
```   139     by (rule summable_comparison_test)
```
```   140 qed
```
```   141
```
```   142 lemma powser_inside:
```
```   143   fixes f :: "nat \<Rightarrow> 'a::{real_normed_div_algebra,banach}"
```
```   144   shows
```
```   145     "summable (\<lambda>n. f n * (x ^ n)) \<Longrightarrow> norm z < norm x \<Longrightarrow>
```
```   146       summable (\<lambda>n. f n * (z ^ n))"
```
```   147   by (rule powser_insidea [THEN summable_norm_cancel])
```
```   148
```
```   149 lemma sum_split_even_odd:
```
```   150   fixes f :: "nat \<Rightarrow> real"
```
```   151   shows
```
```   152     "(\<Sum> i = 0 ..< 2 * n. if even i then f i else g i) =
```
```   153      (\<Sum> i = 0 ..< n. f (2 * i)) + (\<Sum> i = 0 ..< n. g (2 * i + 1))"
```
```   154 proof (induct n)
```
```   155   case 0
```
```   156   then show ?case by simp
```
```   157 next
```
```   158   case (Suc n)
```
```   159   have "(\<Sum> i = 0 ..< 2 * Suc n. if even i then f i else g i) =
```
```   160     (\<Sum> i = 0 ..< n. f (2 * i)) + (\<Sum> i = 0 ..< n. g (2 * i + 1)) + (f (2 * n) + g (2 * n + 1))"
```
```   161     using Suc.hyps unfolding One_nat_def by auto
```
```   162   also have "\<dots> = (\<Sum> i = 0 ..< Suc n. f (2 * i)) + (\<Sum> i = 0 ..< Suc n. g (2 * i + 1))"
```
```   163     by auto
```
```   164   finally show ?case .
```
```   165 qed
```
```   166
```
```   167 lemma sums_if':
```
```   168   fixes g :: "nat \<Rightarrow> real"
```
```   169   assumes "g sums x"
```
```   170   shows "(\<lambda> n. if even n then 0 else g ((n - 1) div 2)) sums x"
```
```   171   unfolding sums_def
```
```   172 proof (rule LIMSEQ_I)
```
```   173   fix r :: real
```
```   174   assume "0 < r"
```
```   175   from `g sums x`[unfolded sums_def, THEN LIMSEQ_D, OF this]
```
```   176   obtain no where no_eq: "\<And> n. n \<ge> no \<Longrightarrow> (norm (setsum g { 0..<n } - x) < r)" by blast
```
```   177
```
```   178   let ?SUM = "\<lambda> m. \<Sum> i = 0 ..< m. if even i then 0 else g ((i - 1) div 2)"
```
```   179   {
```
```   180     fix m
```
```   181     assume "m \<ge> 2 * no"
```
```   182     hence "m div 2 \<ge> no" by auto
```
```   183     have sum_eq: "?SUM (2 * (m div 2)) = setsum g { 0 ..< m div 2 }"
```
```   184       using sum_split_even_odd by auto
```
```   185     hence "(norm (?SUM (2 * (m div 2)) - x) < r)"
```
```   186       using no_eq unfolding sum_eq using `m div 2 \<ge> no` by auto
```
```   187     moreover
```
```   188     have "?SUM (2 * (m div 2)) = ?SUM m"
```
```   189     proof (cases "even m")
```
```   190       case True
```
```   191       show ?thesis
```
```   192         unfolding even_nat_div_two_times_two[OF True, unfolded numeral_2_eq_2[symmetric]] ..
```
```   193     next
```
```   194       case False
```
```   195       hence "even (Suc m)" by auto
```
```   196       from even_nat_div_two_times_two[OF this, unfolded numeral_2_eq_2[symmetric]]
```
```   197         odd_nat_plus_one_div_two[OF False, unfolded numeral_2_eq_2[symmetric]]
```
```   198       have eq: "Suc (2 * (m div 2)) = m" by auto
```
```   199       hence "even (2 * (m div 2))" using `odd m` by auto
```
```   200       have "?SUM m = ?SUM (Suc (2 * (m div 2)))" unfolding eq ..
```
```   201       also have "\<dots> = ?SUM (2 * (m div 2))" using `even (2 * (m div 2))` by auto
```
```   202       finally show ?thesis by auto
```
```   203     qed
```
```   204     ultimately have "(norm (?SUM m - x) < r)" by auto
```
```   205   }
```
```   206   thus "\<exists> no. \<forall> m \<ge> no. norm (?SUM m - x) < r" by blast
```
```   207 qed
```
```   208
```
```   209 lemma sums_if:
```
```   210   fixes g :: "nat \<Rightarrow> real"
```
```   211   assumes "g sums x" and "f sums y"
```
```   212   shows "(\<lambda> n. if even n then f (n div 2) else g ((n - 1) div 2)) sums (x + y)"
```
```   213 proof -
```
```   214   let ?s = "\<lambda> n. if even n then 0 else f ((n - 1) div 2)"
```
```   215   {
```
```   216     fix B T E
```
```   217     have "(if B then (0 :: real) else E) + (if B then T else 0) = (if B then T else E)"
```
```   218       by (cases B) auto
```
```   219   } note if_sum = this
```
```   220   have g_sums: "(\<lambda> n. if even n then 0 else g ((n - 1) div 2)) sums x"
```
```   221     using sums_if'[OF `g sums x`] .
```
```   222   {
```
```   223     have "?s 0 = 0" by auto
```
```   224     have Suc_m1: "\<And> n. Suc n - 1 = n" by auto
```
```   225     have if_eq: "\<And>B T E. (if \<not> B then T else E) = (if B then E else T)" by auto
```
```   226
```
```   227     have "?s sums y" using sums_if'[OF `f sums y`] .
```
```   228     from this[unfolded sums_def, THEN LIMSEQ_Suc]
```
```   229     have "(\<lambda> n. if even n then f (n div 2) else 0) sums y"
```
```   230       unfolding sums_def setsum_shift_lb_Suc0_0_upt[where f="?s", OF `?s 0 = 0`, symmetric]
```
```   231                 image_Suc_atLeastLessThan[symmetric] setsum_reindex[OF inj_Suc, unfolded comp_def]
```
```   232                 even_Suc Suc_m1 if_eq .
```
```   233   }
```
```   234   from sums_add[OF g_sums this] show ?thesis unfolding if_sum .
```
```   235 qed
```
```   236
```
```   237 subsection {* Alternating series test / Leibniz formula *}
```
```   238
```
```   239 lemma sums_alternating_upper_lower:
```
```   240   fixes a :: "nat \<Rightarrow> real"
```
```   241   assumes mono: "\<And>n. a (Suc n) \<le> a n" and a_pos: "\<And>n. 0 \<le> a n" and "a ----> 0"
```
```   242   shows "\<exists>l. ((\<forall>n. (\<Sum>i=0..<2*n. -1^i*a i) \<le> l) \<and> (\<lambda> n. \<Sum>i=0..<2*n. -1^i*a i) ----> l) \<and>
```
```   243              ((\<forall>n. l \<le> (\<Sum>i=0..<2*n + 1. -1^i*a i)) \<and> (\<lambda> n. \<Sum>i=0..<2*n + 1. -1^i*a i) ----> l)"
```
```   244   (is "\<exists>l. ((\<forall>n. ?f n \<le> l) \<and> _) \<and> ((\<forall>n. l \<le> ?g n) \<and> _)")
```
```   245 proof (rule nested_sequence_unique)
```
```   246   have fg_diff: "\<And>n. ?f n - ?g n = - a (2 * n)" unfolding One_nat_def by auto
```
```   247
```
```   248   show "\<forall>n. ?f n \<le> ?f (Suc n)"
```
```   249   proof
```
```   250     fix n
```
```   251     show "?f n \<le> ?f (Suc n)" using mono[of "2*n"] by auto
```
```   252   qed
```
```   253   show "\<forall>n. ?g (Suc n) \<le> ?g n"
```
```   254   proof
```
```   255     fix n
```
```   256     show "?g (Suc n) \<le> ?g n" using mono[of "Suc (2*n)"]
```
```   257       unfolding One_nat_def by auto
```
```   258   qed
```
```   259   show "\<forall>n. ?f n \<le> ?g n"
```
```   260   proof
```
```   261     fix n
```
```   262     show "?f n \<le> ?g n" using fg_diff a_pos
```
```   263       unfolding One_nat_def by auto
```
```   264   qed
```
```   265   show "(\<lambda>n. ?f n - ?g n) ----> 0" unfolding fg_diff
```
```   266   proof (rule LIMSEQ_I)
```
```   267     fix r :: real
```
```   268     assume "0 < r"
```
```   269     with `a ----> 0`[THEN LIMSEQ_D] obtain N where "\<And> n. n \<ge> N \<Longrightarrow> norm (a n - 0) < r"
```
```   270       by auto
```
```   271     hence "\<forall>n \<ge> N. norm (- a (2 * n) - 0) < r" by auto
```
```   272     thus "\<exists>N. \<forall>n \<ge> N. norm (- a (2 * n) - 0) < r" by auto
```
```   273   qed
```
```   274 qed
```
```   275
```
```   276 lemma summable_Leibniz':
```
```   277   fixes a :: "nat \<Rightarrow> real"
```
```   278   assumes a_zero: "a ----> 0"
```
```   279     and a_pos: "\<And> n. 0 \<le> a n"
```
```   280     and a_monotone: "\<And> n. a (Suc n) \<le> a n"
```
```   281   shows summable: "summable (\<lambda> n. (-1)^n * a n)"
```
```   282     and "\<And>n. (\<Sum>i=0..<2*n. (-1)^i*a i) \<le> (\<Sum>i. (-1)^i*a i)"
```
```   283     and "(\<lambda>n. \<Sum>i=0..<2*n. (-1)^i*a i) ----> (\<Sum>i. (-1)^i*a i)"
```
```   284     and "\<And>n. (\<Sum>i. (-1)^i*a i) \<le> (\<Sum>i=0..<2*n+1. (-1)^i*a i)"
```
```   285     and "(\<lambda>n. \<Sum>i=0..<2*n+1. (-1)^i*a i) ----> (\<Sum>i. (-1)^i*a i)"
```
```   286 proof -
```
```   287   let ?S = "\<lambda>n. (-1)^n * a n"
```
```   288   let ?P = "\<lambda>n. \<Sum>i=0..<n. ?S i"
```
```   289   let ?f = "\<lambda>n. ?P (2 * n)"
```
```   290   let ?g = "\<lambda>n. ?P (2 * n + 1)"
```
```   291   obtain l :: real
```
```   292     where below_l: "\<forall> n. ?f n \<le> l"
```
```   293       and "?f ----> l"
```
```   294       and above_l: "\<forall> n. l \<le> ?g n"
```
```   295       and "?g ----> l"
```
```   296     using sums_alternating_upper_lower[OF a_monotone a_pos a_zero] by blast
```
```   297
```
```   298   let ?Sa = "\<lambda>m. \<Sum> n = 0..<m. ?S n"
```
```   299   have "?Sa ----> l"
```
```   300   proof (rule LIMSEQ_I)
```
```   301     fix r :: real
```
```   302     assume "0 < r"
```
```   303     with `?f ----> l`[THEN LIMSEQ_D]
```
```   304     obtain f_no where f: "\<And> n. n \<ge> f_no \<Longrightarrow> norm (?f n - l) < r" by auto
```
```   305
```
```   306     from `0 < r` `?g ----> l`[THEN LIMSEQ_D]
```
```   307     obtain g_no where g: "\<And> n. n \<ge> g_no \<Longrightarrow> norm (?g n - l) < r" by auto
```
```   308
```
```   309     {
```
```   310       fix n :: nat
```
```   311       assume "n \<ge> (max (2 * f_no) (2 * g_no))"
```
```   312       hence "n \<ge> 2 * f_no" and "n \<ge> 2 * g_no" by auto
```
```   313       have "norm (?Sa n - l) < r"
```
```   314       proof (cases "even n")
```
```   315         case True
```
```   316         from even_nat_div_two_times_two[OF this]
```
```   317         have n_eq: "2 * (n div 2) = n"
```
```   318           unfolding numeral_2_eq_2[symmetric] by auto
```
```   319         with `n \<ge> 2 * f_no` have "n div 2 \<ge> f_no"
```
```   320           by auto
```
```   321         from f[OF this] show ?thesis
```
```   322           unfolding n_eq atLeastLessThanSuc_atLeastAtMost .
```
```   323       next
```
```   324         case False
```
```   325         hence "even (n - 1)" by simp
```
```   326         from even_nat_div_two_times_two[OF this]
```
```   327         have n_eq: "2 * ((n - 1) div 2) = n - 1"
```
```   328           unfolding numeral_2_eq_2[symmetric] by auto
```
```   329         hence range_eq: "n - 1 + 1 = n"
```
```   330           using odd_pos[OF False] by auto
```
```   331
```
```   332         from n_eq `n \<ge> 2 * g_no` have "(n - 1) div 2 \<ge> g_no"
```
```   333           by auto
```
```   334         from g[OF this] show ?thesis
```
```   335           unfolding n_eq atLeastLessThanSuc_atLeastAtMost range_eq .
```
```   336       qed
```
```   337     }
```
```   338     thus "\<exists>no. \<forall>n \<ge> no. norm (?Sa n - l) < r" by blast
```
```   339   qed
```
```   340   hence sums_l: "(\<lambda>i. (-1)^i * a i) sums l"
```
```   341     unfolding sums_def atLeastLessThanSuc_atLeastAtMost[symmetric] .
```
```   342   thus "summable ?S" using summable_def by auto
```
```   343
```
```   344   have "l = suminf ?S" using sums_unique[OF sums_l] .
```
```   345
```
```   346   fix n
```
```   347   show "suminf ?S \<le> ?g n"
```
```   348     unfolding sums_unique[OF sums_l, symmetric] using above_l by auto
```
```   349   show "?f n \<le> suminf ?S"
```
```   350     unfolding sums_unique[OF sums_l, symmetric] using below_l by auto
```
```   351   show "?g ----> suminf ?S"
```
```   352     using `?g ----> l` `l = suminf ?S` by auto
```
```   353   show "?f ----> suminf ?S"
```
```   354     using `?f ----> l` `l = suminf ?S` by auto
```
```   355 qed
```
```   356
```
```   357 theorem summable_Leibniz:
```
```   358   fixes a :: "nat \<Rightarrow> real"
```
```   359   assumes a_zero: "a ----> 0" and "monoseq a"
```
```   360   shows "summable (\<lambda> n. (-1)^n * a n)" (is "?summable")
```
```   361     and "0 < a 0 \<longrightarrow>
```
```   362       (\<forall>n. (\<Sum>i. -1^i*a i) \<in> { \<Sum>i=0..<2*n. -1^i * a i .. \<Sum>i=0..<2*n+1. -1^i * a i})" (is "?pos")
```
```   363     and "a 0 < 0 \<longrightarrow>
```
```   364       (\<forall>n. (\<Sum>i. -1^i*a i) \<in> { \<Sum>i=0..<2*n+1. -1^i * a i .. \<Sum>i=0..<2*n. -1^i * a i})" (is "?neg")
```
```   365     and "(\<lambda>n. \<Sum>i=0..<2*n. -1^i*a i) ----> (\<Sum>i. -1^i*a i)" (is "?f")
```
```   366     and "(\<lambda>n. \<Sum>i=0..<2*n+1. -1^i*a i) ----> (\<Sum>i. -1^i*a i)" (is "?g")
```
```   367 proof -
```
```   368   have "?summable \<and> ?pos \<and> ?neg \<and> ?f \<and> ?g"
```
```   369   proof (cases "(\<forall> n. 0 \<le> a n) \<and> (\<forall>m. \<forall>n\<ge>m. a n \<le> a m)")
```
```   370     case True
```
```   371     hence ord: "\<And>n m. m \<le> n \<Longrightarrow> a n \<le> a m" and ge0: "\<And> n. 0 \<le> a n"
```
```   372       by auto
```
```   373     {
```
```   374       fix n
```
```   375       have "a (Suc n) \<le> a n"
```
```   376         using ord[where n="Suc n" and m=n] by auto
```
```   377     } note mono = this
```
```   378     note leibniz = summable_Leibniz'[OF `a ----> 0` ge0]
```
```   379     from leibniz[OF mono]
```
```   380     show ?thesis using `0 \<le> a 0` by auto
```
```   381   next
```
```   382     let ?a = "\<lambda> n. - a n"
```
```   383     case False
```
```   384     with monoseq_le[OF `monoseq a` `a ----> 0`]
```
```   385     have "(\<forall> n. a n \<le> 0) \<and> (\<forall>m. \<forall>n\<ge>m. a m \<le> a n)" by auto
```
```   386     hence ord: "\<And>n m. m \<le> n \<Longrightarrow> ?a n \<le> ?a m" and ge0: "\<And> n. 0 \<le> ?a n"
```
```   387       by auto
```
```   388     {
```
```   389       fix n
```
```   390       have "?a (Suc n) \<le> ?a n" using ord[where n="Suc n" and m=n]
```
```   391         by auto
```
```   392     } note monotone = this
```
```   393     note leibniz =
```
```   394       summable_Leibniz'[OF _ ge0, of "\<lambda>x. x",
```
```   395         OF tendsto_minus[OF `a ----> 0`, unfolded minus_zero] monotone]
```
```   396     have "summable (\<lambda> n. (-1)^n * ?a n)"
```
```   397       using leibniz(1) by auto
```
```   398     then obtain l where "(\<lambda> n. (-1)^n * ?a n) sums l"
```
```   399       unfolding summable_def by auto
```
```   400     from this[THEN sums_minus] have "(\<lambda> n. (-1)^n * a n) sums -l"
```
```   401       by auto
```
```   402     hence ?summable unfolding summable_def by auto
```
```   403     moreover
```
```   404     have "\<And>a b :: real. \<bar>- a - - b\<bar> = \<bar>a - b\<bar>"
```
```   405       unfolding minus_diff_minus by auto
```
```   406
```
```   407     from suminf_minus[OF leibniz(1), unfolded mult_minus_right minus_minus]
```
```   408     have move_minus: "(\<Sum>n. - (-1 ^ n * a n)) = - (\<Sum>n. -1 ^ n * a n)"
```
```   409       by auto
```
```   410
```
```   411     have ?pos using `0 \<le> ?a 0` by auto
```
```   412     moreover have ?neg
```
```   413       using leibniz(2,4)
```
```   414       unfolding mult_minus_right setsum_negf move_minus neg_le_iff_le
```
```   415       by auto
```
```   416     moreover have ?f and ?g
```
```   417       using leibniz(3,5)[unfolded mult_minus_right setsum_negf move_minus, THEN tendsto_minus_cancel]
```
```   418       by auto
```
```   419     ultimately show ?thesis by auto
```
```   420   qed
```
```   421   then show ?summable and ?pos and ?neg and ?f and ?g
```
```   422     by safe
```
```   423 qed
```
```   424
```
```   425 subsection {* Term-by-Term Differentiability of Power Series *}
```
```   426
```
```   427 definition diffs :: "(nat => 'a::ring_1) => nat => 'a"
```
```   428   where "diffs c = (\<lambda>n. of_nat (Suc n) * c(Suc n))"
```
```   429
```
```   430 text{*Lemma about distributing negation over it*}
```
```   431 lemma diffs_minus: "diffs (\<lambda>n. - c n) = (\<lambda>n. - diffs c n)"
```
```   432   by (simp add: diffs_def)
```
```   433
```
```   434 lemma sums_Suc_imp:
```
```   435   assumes f: "f 0 = 0"
```
```   436   shows "(\<lambda>n. f (Suc n)) sums s \<Longrightarrow> (\<lambda>n. f n) sums s"
```
```   437   unfolding sums_def
```
```   438   apply (rule LIMSEQ_imp_Suc)
```
```   439   apply (subst setsum_shift_lb_Suc0_0_upt [where f=f, OF f, symmetric])
```
```   440   apply (simp only: setsum_shift_bounds_Suc_ivl)
```
```   441   done
```
```   442
```
```   443 lemma diffs_equiv:
```
```   444   fixes x :: "'a::{real_normed_vector, ring_1}"
```
```   445   shows "summable (\<lambda>n. (diffs c)(n) * (x ^ n)) \<Longrightarrow>
```
```   446       (\<lambda>n. of_nat n * c(n) * (x ^ (n - Suc 0))) sums
```
```   447          (\<Sum>n. (diffs c)(n) * (x ^ n))"
```
```   448   unfolding diffs_def
```
```   449   by (simp add: summable_sums sums_Suc_imp)
```
```   450
```
```   451 lemma lemma_termdiff1:
```
```   452   fixes z :: "'a :: {monoid_mult,comm_ring}" shows
```
```   453   "(\<Sum>p=0..<m. (((z + h) ^ (m - p)) * (z ^ p)) - (z ^ m)) =
```
```   454    (\<Sum>p=0..<m. (z ^ p) * (((z + h) ^ (m - p)) - (z ^ (m - p))))"
```
```   455   by (auto simp add: algebra_simps power_add [symmetric])
```
```   456
```
```   457 lemma sumr_diff_mult_const2:
```
```   458   "setsum f {0..<n} - of_nat n * (r::'a::ring_1) = (\<Sum>i = 0..<n. f i - r)"
```
```   459   by (simp add: setsum_subtractf)
```
```   460
```
```   461 lemma lemma_termdiff2:
```
```   462   fixes h :: "'a :: {field}"
```
```   463   assumes h: "h \<noteq> 0"
```
```   464   shows
```
```   465     "((z + h) ^ n - z ^ n) / h - of_nat n * z ^ (n - Suc 0) =
```
```   466      h * (\<Sum>p=0..< n - Suc 0. \<Sum>q=0..< n - Suc 0 - p.
```
```   467           (z + h) ^ q * z ^ (n - 2 - q))" (is "?lhs = ?rhs")
```
```   468   apply (subgoal_tac "h * ?lhs = h * ?rhs", simp add: h)
```
```   469   apply (simp add: right_diff_distrib diff_divide_distrib h)
```
```   470   apply (simp add: mult_assoc [symmetric])
```
```   471   apply (cases "n", simp)
```
```   472   apply (simp add: lemma_realpow_diff_sumr2 h
```
```   473                    right_diff_distrib [symmetric] mult_assoc
```
```   474               del: power_Suc setsum_op_ivl_Suc of_nat_Suc)
```
```   475   apply (subst lemma_realpow_rev_sumr)
```
```   476   apply (subst sumr_diff_mult_const2)
```
```   477   apply simp
```
```   478   apply (simp only: lemma_termdiff1 setsum_right_distrib)
```
```   479   apply (rule setsum_cong [OF refl])
```
```   480   apply (simp add: less_iff_Suc_add)
```
```   481   apply (clarify)
```
```   482   apply (simp add: setsum_right_distrib lemma_realpow_diff_sumr2 mult_ac
```
```   483               del: setsum_op_ivl_Suc power_Suc)
```
```   484   apply (subst mult_assoc [symmetric], subst power_add [symmetric])
```
```   485   apply (simp add: mult_ac)
```
```   486   done
```
```   487
```
```   488 lemma real_setsum_nat_ivl_bounded2:
```
```   489   fixes K :: "'a::linordered_semidom"
```
```   490   assumes f: "\<And>p::nat. p < n \<Longrightarrow> f p \<le> K"
```
```   491     and K: "0 \<le> K"
```
```   492   shows "setsum f {0..<n-k} \<le> of_nat n * K"
```
```   493   apply (rule order_trans [OF setsum_mono])
```
```   494   apply (rule f, simp)
```
```   495   apply (simp add: mult_right_mono K)
```
```   496   done
```
```   497
```
```   498 lemma lemma_termdiff3:
```
```   499   fixes h z :: "'a::{real_normed_field}"
```
```   500   assumes 1: "h \<noteq> 0"
```
```   501     and 2: "norm z \<le> K"
```
```   502     and 3: "norm (z + h) \<le> K"
```
```   503   shows "norm (((z + h) ^ n - z ^ n) / h - of_nat n * z ^ (n - Suc 0))
```
```   504           \<le> of_nat n * of_nat (n - Suc 0) * K ^ (n - 2) * norm h"
```
```   505 proof -
```
```   506   have "norm (((z + h) ^ n - z ^ n) / h - of_nat n * z ^ (n - Suc 0)) =
```
```   507         norm (\<Sum>p = 0..<n - Suc 0. \<Sum>q = 0..<n - Suc 0 - p.
```
```   508           (z + h) ^ q * z ^ (n - 2 - q)) * norm h"
```
```   509     by (metis (lifting, no_types) lemma_termdiff2 [OF 1] mult_commute norm_mult)
```
```   510   also have "\<dots> \<le> of_nat n * (of_nat (n - Suc 0) * K ^ (n - 2)) * norm h"
```
```   511   proof (rule mult_right_mono [OF _ norm_ge_zero])
```
```   512     from norm_ge_zero 2 have K: "0 \<le> K"
```
```   513       by (rule order_trans)
```
```   514     have le_Kn: "\<And>i j n. i + j = n \<Longrightarrow> norm ((z + h) ^ i * z ^ j) \<le> K ^ n"
```
```   515       apply (erule subst)
```
```   516       apply (simp only: norm_mult norm_power power_add)
```
```   517       apply (intro mult_mono power_mono 2 3 norm_ge_zero zero_le_power K)
```
```   518       done
```
```   519     show "norm (\<Sum>p = 0..<n - Suc 0. \<Sum>q = 0..<n - Suc 0 - p. (z + h) ^ q * z ^ (n - 2 - q))
```
```   520           \<le> of_nat n * (of_nat (n - Suc 0) * K ^ (n - 2))"
```
```   521       apply (intro
```
```   522          order_trans [OF norm_setsum]
```
```   523          real_setsum_nat_ivl_bounded2
```
```   524          mult_nonneg_nonneg
```
```   525          of_nat_0_le_iff
```
```   526          zero_le_power K)
```
```   527       apply (rule le_Kn, simp)
```
```   528       done
```
```   529   qed
```
```   530   also have "\<dots> = of_nat n * of_nat (n - Suc 0) * K ^ (n - 2) * norm h"
```
```   531     by (simp only: mult_assoc)
```
```   532   finally show ?thesis .
```
```   533 qed
```
```   534
```
```   535 lemma lemma_termdiff4:
```
```   536   fixes f :: "'a::real_normed_vector \<Rightarrow> 'b::real_normed_vector"
```
```   537   assumes k: "0 < (k::real)"
```
```   538     and le: "\<And>h. \<lbrakk>h \<noteq> 0; norm h < k\<rbrakk> \<Longrightarrow> norm (f h) \<le> K * norm h"
```
```   539   shows "f -- 0 --> 0"
```
```   540 proof (rule tendsto_norm_zero_cancel)
```
```   541   show "(\<lambda>h. norm (f h)) -- 0 --> 0"
```
```   542   proof (rule real_tendsto_sandwich)
```
```   543     show "eventually (\<lambda>h. 0 \<le> norm (f h)) (at 0)"
```
```   544       by simp
```
```   545     show "eventually (\<lambda>h. norm (f h) \<le> K * norm h) (at 0)"
```
```   546       using k by (auto simp add: eventually_at dist_norm le)
```
```   547     show "(\<lambda>h. 0) -- (0::'a) --> (0::real)"
```
```   548       by (rule tendsto_const)
```
```   549     have "(\<lambda>h. K * norm h) -- (0::'a) --> K * norm (0::'a)"
```
```   550       by (intro tendsto_intros)
```
```   551     then show "(\<lambda>h. K * norm h) -- (0::'a) --> 0"
```
```   552       by simp
```
```   553   qed
```
```   554 qed
```
```   555
```
```   556 lemma lemma_termdiff5:
```
```   557   fixes g :: "'a::real_normed_vector \<Rightarrow> nat \<Rightarrow> 'b::banach"
```
```   558   assumes k: "0 < (k::real)"
```
```   559   assumes f: "summable f"
```
```   560   assumes le: "\<And>h n. \<lbrakk>h \<noteq> 0; norm h < k\<rbrakk> \<Longrightarrow> norm (g h n) \<le> f n * norm h"
```
```   561   shows "(\<lambda>h. suminf (g h)) -- 0 --> 0"
```
```   562 proof (rule lemma_termdiff4 [OF k])
```
```   563   fix h::'a
```
```   564   assume "h \<noteq> 0" and "norm h < k"
```
```   565   hence A: "\<forall>n. norm (g h n) \<le> f n * norm h"
```
```   566     by (simp add: le)
```
```   567   hence "\<exists>N. \<forall>n\<ge>N. norm (norm (g h n)) \<le> f n * norm h"
```
```   568     by simp
```
```   569   moreover from f have B: "summable (\<lambda>n. f n * norm h)"
```
```   570     by (rule summable_mult2)
```
```   571   ultimately have C: "summable (\<lambda>n. norm (g h n))"
```
```   572     by (rule summable_comparison_test)
```
```   573   hence "norm (suminf (g h)) \<le> (\<Sum>n. norm (g h n))"
```
```   574     by (rule summable_norm)
```
```   575   also from A C B have "(\<Sum>n. norm (g h n)) \<le> (\<Sum>n. f n * norm h)"
```
```   576     by (rule summable_le)
```
```   577   also from f have "(\<Sum>n. f n * norm h) = suminf f * norm h"
```
```   578     by (rule suminf_mult2 [symmetric])
```
```   579   finally show "norm (suminf (g h)) \<le> suminf f * norm h" .
```
```   580 qed
```
```   581
```
```   582
```
```   583 text{* FIXME: Long proofs*}
```
```   584
```
```   585 lemma termdiffs_aux:
```
```   586   fixes x :: "'a::{real_normed_field,banach}"
```
```   587   assumes 1: "summable (\<lambda>n. diffs (diffs c) n * K ^ n)"
```
```   588     and 2: "norm x < norm K"
```
```   589   shows "(\<lambda>h. \<Sum>n. c n * (((x + h) ^ n - x ^ n) / h
```
```   590              - of_nat n * x ^ (n - Suc 0))) -- 0 --> 0"
```
```   591 proof -
```
```   592   from dense [OF 2]
```
```   593   obtain r where r1: "norm x < r" and r2: "r < norm K" by fast
```
```   594   from norm_ge_zero r1 have r: "0 < r"
```
```   595     by (rule order_le_less_trans)
```
```   596   hence r_neq_0: "r \<noteq> 0" by simp
```
```   597   show ?thesis
```
```   598   proof (rule lemma_termdiff5)
```
```   599     show "0 < r - norm x" using r1 by simp
```
```   600     from r r2 have "norm (of_real r::'a) < norm K"
```
```   601       by simp
```
```   602     with 1 have "summable (\<lambda>n. norm (diffs (diffs c) n * (of_real r ^ n)))"
```
```   603       by (rule powser_insidea)
```
```   604     hence "summable (\<lambda>n. diffs (diffs (\<lambda>n. norm (c n))) n * r ^ n)"
```
```   605       using r
```
```   606       by (simp add: diffs_def norm_mult norm_power del: of_nat_Suc)
```
```   607     hence "summable (\<lambda>n. of_nat n * diffs (\<lambda>n. norm (c n)) n * r ^ (n - Suc 0))"
```
```   608       by (rule diffs_equiv [THEN sums_summable])
```
```   609     also have "(\<lambda>n. of_nat n * diffs (\<lambda>n. norm (c n)) n * r ^ (n - Suc 0)) =
```
```   610       (\<lambda>n. diffs (\<lambda>m. of_nat (m - Suc 0) * norm (c m) * inverse r) n * (r ^ n))"
```
```   611       apply (rule ext)
```
```   612       apply (simp add: diffs_def)
```
```   613       apply (case_tac n, simp_all add: r_neq_0)
```
```   614       done
```
```   615     finally have "summable
```
```   616       (\<lambda>n. of_nat n * (of_nat (n - Suc 0) * norm (c n) * inverse r) * r ^ (n - Suc 0))"
```
```   617       by (rule diffs_equiv [THEN sums_summable])
```
```   618     also have
```
```   619       "(\<lambda>n. of_nat n * (of_nat (n - Suc 0) * norm (c n) * inverse r) *
```
```   620            r ^ (n - Suc 0)) =
```
```   621        (\<lambda>n. norm (c n) * of_nat n * of_nat (n - Suc 0) * r ^ (n - 2))"
```
```   622       apply (rule ext)
```
```   623       apply (case_tac "n", simp)
```
```   624       apply (rename_tac nat)
```
```   625       apply (case_tac "nat", simp)
```
```   626       apply (simp add: r_neq_0)
```
```   627       done
```
```   628     finally
```
```   629     show "summable (\<lambda>n. norm (c n) * of_nat n * of_nat (n - Suc 0) * r ^ (n - 2))" .
```
```   630   next
```
```   631     fix h::'a and n::nat
```
```   632     assume h: "h \<noteq> 0"
```
```   633     assume "norm h < r - norm x"
```
```   634     hence "norm x + norm h < r" by simp
```
```   635     with norm_triangle_ineq have xh: "norm (x + h) < r"
```
```   636       by (rule order_le_less_trans)
```
```   637     show "norm (c n * (((x + h) ^ n - x ^ n) / h - of_nat n * x ^ (n - Suc 0)))
```
```   638           \<le> norm (c n) * of_nat n * of_nat (n - Suc 0) * r ^ (n - 2) * norm h"
```
```   639       apply (simp only: norm_mult mult_assoc)
```
```   640       apply (rule mult_left_mono [OF _ norm_ge_zero])
```
```   641       apply (simp add: mult_assoc [symmetric])
```
```   642       apply (metis h lemma_termdiff3 less_eq_real_def r1 xh)
```
```   643       done
```
```   644   qed
```
```   645 qed
```
```   646
```
```   647 lemma termdiffs:
```
```   648   fixes K x :: "'a::{real_normed_field,banach}"
```
```   649   assumes 1: "summable (\<lambda>n. c n * K ^ n)"
```
```   650       and 2: "summable (\<lambda>n. (diffs c) n * K ^ n)"
```
```   651       and 3: "summable (\<lambda>n. (diffs (diffs c)) n * K ^ n)"
```
```   652       and 4: "norm x < norm K"
```
```   653   shows "DERIV (\<lambda>x. \<Sum>n. c n * x ^ n) x :> (\<Sum>n. (diffs c) n * x ^ n)"
```
```   654   unfolding deriv_def
```
```   655 proof (rule LIM_zero_cancel)
```
```   656   show "(\<lambda>h. (suminf (\<lambda>n. c n * (x + h) ^ n) - suminf (\<lambda>n. c n * x ^ n)) / h
```
```   657             - suminf (\<lambda>n. diffs c n * x ^ n)) -- 0 --> 0"
```
```   658   proof (rule LIM_equal2)
```
```   659     show "0 < norm K - norm x" using 4 by (simp add: less_diff_eq)
```
```   660   next
```
```   661     fix h :: 'a
```
```   662     assume "norm (h - 0) < norm K - norm x"
```
```   663     hence "norm x + norm h < norm K" by simp
```
```   664     hence 5: "norm (x + h) < norm K"
```
```   665       by (rule norm_triangle_ineq [THEN order_le_less_trans])
```
```   666     have "summable (\<lambda>n. c n * x ^ n)"
```
```   667       and "summable (\<lambda>n. c n * (x + h) ^ n)"
```
```   668       and "summable (\<lambda>n. diffs c n * x ^ n)"
```
```   669       using 1 2 4 5 by (auto elim: powser_inside)
```
```   670     then have "((\<Sum>n. c n * (x + h) ^ n) - (\<Sum>n. c n * x ^ n)) / h - (\<Sum>n. diffs c n * x ^ n) =
```
```   671           (\<Sum>n. (c n * (x + h) ^ n - c n * x ^ n) / h - of_nat n * c n * x ^ (n - Suc 0))"
```
```   672       by (intro sums_unique sums_diff sums_divide diffs_equiv summable_sums)
```
```   673     then show "((\<Sum>n. c n * (x + h) ^ n) - (\<Sum>n. c n * x ^ n)) / h - (\<Sum>n. diffs c n * x ^ n) =
```
```   674           (\<Sum>n. c n * (((x + h) ^ n - x ^ n) / h - of_nat n * x ^ (n - Suc 0)))"
```
```   675       by (simp add: algebra_simps)
```
```   676   next
```
```   677     show "(\<lambda>h. \<Sum>n. c n * (((x + h) ^ n - x ^ n) / h - of_nat n * x ^ (n - Suc 0))) -- 0 --> 0"
```
```   678       by (rule termdiffs_aux [OF 3 4])
```
```   679   qed
```
```   680 qed
```
```   681
```
```   682
```
```   683 subsection {* Derivability of power series *}
```
```   684
```
```   685 lemma DERIV_series':
```
```   686   fixes f :: "real \<Rightarrow> nat \<Rightarrow> real"
```
```   687   assumes DERIV_f: "\<And> n. DERIV (\<lambda> x. f x n) x0 :> (f' x0 n)"
```
```   688     and allf_summable: "\<And> x. x \<in> {a <..< b} \<Longrightarrow> summable (f x)" and x0_in_I: "x0 \<in> {a <..< b}"
```
```   689     and "summable (f' x0)"
```
```   690     and "summable L"
```
```   691     and L_def: "\<And>n x y. \<lbrakk> x \<in> { a <..< b} ; y \<in> { a <..< b} \<rbrakk> \<Longrightarrow> \<bar>f x n - f y n\<bar> \<le> L n * \<bar>x - y\<bar>"
```
```   692   shows "DERIV (\<lambda> x. suminf (f x)) x0 :> (suminf (f' x0))"
```
```   693   unfolding deriv_def
```
```   694 proof (rule LIM_I)
```
```   695   fix r :: real
```
```   696   assume "0 < r" hence "0 < r/3" by auto
```
```   697
```
```   698   obtain N_L where N_L: "\<And> n. N_L \<le> n \<Longrightarrow> \<bar> \<Sum> i. L (i + n) \<bar> < r/3"
```
```   699     using suminf_exist_split[OF `0 < r/3` `summable L`] by auto
```
```   700
```
```   701   obtain N_f' where N_f': "\<And> n. N_f' \<le> n \<Longrightarrow> \<bar> \<Sum> i. f' x0 (i + n) \<bar> < r/3"
```
```   702     using suminf_exist_split[OF `0 < r/3` `summable (f' x0)`] by auto
```
```   703
```
```   704   let ?N = "Suc (max N_L N_f')"
```
```   705   have "\<bar> \<Sum> i. f' x0 (i + ?N) \<bar> < r/3" (is "?f'_part < r/3") and
```
```   706     L_estimate: "\<bar> \<Sum> i. L (i + ?N) \<bar> < r/3" using N_L[of "?N"] and N_f' [of "?N"] by auto
```
```   707
```
```   708   let ?diff = "\<lambda>i x. (f (x0 + x) i - f x0 i) / x"
```
```   709
```
```   710   let ?r = "r / (3 * real ?N)"
```
```   711   have "0 < 3 * real ?N" by auto
```
```   712   from divide_pos_pos[OF `0 < r` this]
```
```   713   have "0 < ?r" .
```
```   714
```
```   715   let "?s n" = "SOME s. 0 < s \<and> (\<forall> x. x \<noteq> 0 \<and> \<bar> x \<bar> < s \<longrightarrow> \<bar> ?diff n x - f' x0 n \<bar> < ?r)"
```
```   716   def S' \<equiv> "Min (?s ` { 0 ..< ?N })"
```
```   717
```
```   718   have "0 < S'" unfolding S'_def
```
```   719   proof (rule iffD2[OF Min_gr_iff])
```
```   720     show "\<forall>x \<in> (?s ` { 0 ..< ?N }). 0 < x"
```
```   721     proof
```
```   722       fix x
```
```   723       assume "x \<in> ?s ` {0..<?N}"
```
```   724       then obtain n where "x = ?s n" and "n \<in> {0..<?N}"
```
```   725         using image_iff[THEN iffD1] by blast
```
```   726       from DERIV_D[OF DERIV_f[where n=n], THEN LIM_D, OF `0 < ?r`, unfolded real_norm_def]
```
```   727       obtain s where s_bound: "0 < s \<and> (\<forall>x. x \<noteq> 0 \<and> \<bar>x\<bar> < s \<longrightarrow> \<bar>?diff n x - f' x0 n\<bar> < ?r)"
```
```   728         by auto
```
```   729       have "0 < ?s n" by (rule someI2[where a=s]) (auto simp add: s_bound)
```
```   730       thus "0 < x" unfolding `x = ?s n` .
```
```   731     qed
```
```   732   qed auto
```
```   733
```
```   734   def S \<equiv> "min (min (x0 - a) (b - x0)) S'"
```
```   735   hence "0 < S" and S_a: "S \<le> x0 - a" and S_b: "S \<le> b - x0"
```
```   736     and "S \<le> S'" using x0_in_I and `0 < S'`
```
```   737     by auto
```
```   738
```
```   739   {
```
```   740     fix x
```
```   741     assume "x \<noteq> 0" and "\<bar> x \<bar> < S"
```
```   742     hence x_in_I: "x0 + x \<in> { a <..< b }"
```
```   743       using S_a S_b by auto
```
```   744
```
```   745     note diff_smbl = summable_diff[OF allf_summable[OF x_in_I] allf_summable[OF x0_in_I]]
```
```   746     note div_smbl = summable_divide[OF diff_smbl]
```
```   747     note all_smbl = summable_diff[OF div_smbl `summable (f' x0)`]
```
```   748     note ign = summable_ignore_initial_segment[where k="?N"]
```
```   749     note diff_shft_smbl = summable_diff[OF ign[OF allf_summable[OF x_in_I]] ign[OF allf_summable[OF x0_in_I]]]
```
```   750     note div_shft_smbl = summable_divide[OF diff_shft_smbl]
```
```   751     note all_shft_smbl = summable_diff[OF div_smbl ign[OF `summable (f' x0)`]]
```
```   752
```
```   753     {
```
```   754       fix n
```
```   755       have "\<bar> ?diff (n + ?N) x \<bar> \<le> L (n + ?N) * \<bar> (x0 + x) - x0 \<bar> / \<bar> x \<bar>"
```
```   756         using divide_right_mono[OF L_def[OF x_in_I x0_in_I] abs_ge_zero]
```
```   757         unfolding abs_divide .
```
```   758       hence "\<bar> (\<bar>?diff (n + ?N) x \<bar>) \<bar> \<le> L (n + ?N)"
```
```   759         using `x \<noteq> 0` by auto
```
```   760     } note L_ge = summable_le2[OF allI[OF this] ign[OF `summable L`]]
```
```   761     from order_trans[OF summable_rabs[OF conjunct1[OF L_ge]] L_ge[THEN conjunct2]]
```
```   762     have "\<bar> \<Sum> i. ?diff (i + ?N) x \<bar> \<le> (\<Sum> i. L (i + ?N))" .
```
```   763     hence "\<bar> \<Sum> i. ?diff (i + ?N) x \<bar> \<le> r / 3" (is "?L_part \<le> r/3")
```
```   764       using L_estimate by auto
```
```   765
```
```   766     have "\<bar>\<Sum>n \<in> { 0 ..< ?N}. ?diff n x - f' x0 n \<bar> \<le>
```
```   767       (\<Sum>n \<in> { 0 ..< ?N}. \<bar>?diff n x - f' x0 n \<bar>)" ..
```
```   768     also have "\<dots> < (\<Sum>n \<in> { 0 ..< ?N}. ?r)"
```
```   769     proof (rule setsum_strict_mono)
```
```   770       fix n
```
```   771       assume "n \<in> { 0 ..< ?N}"
```
```   772       have "\<bar>x\<bar> < S" using `\<bar>x\<bar> < S` .
```
```   773       also have "S \<le> S'" using `S \<le> S'` .
```
```   774       also have "S' \<le> ?s n" unfolding S'_def
```
```   775       proof (rule Min_le_iff[THEN iffD2])
```
```   776         have "?s n \<in> (?s ` {0..<?N}) \<and> ?s n \<le> ?s n"
```
```   777           using `n \<in> { 0 ..< ?N}` by auto
```
```   778         thus "\<exists> a \<in> (?s ` {0..<?N}). a \<le> ?s n" by blast
```
```   779       qed auto
```
```   780       finally have "\<bar>x\<bar> < ?s n" .
```
```   781
```
```   782       from DERIV_D[OF DERIV_f[where n=n], THEN LIM_D, OF `0 < ?r`, unfolded real_norm_def diff_0_right, unfolded some_eq_ex[symmetric], THEN conjunct2]
```
```   783       have "\<forall>x. x \<noteq> 0 \<and> \<bar>x\<bar> < ?s n \<longrightarrow> \<bar>?diff n x - f' x0 n\<bar> < ?r" .
```
```   784       with `x \<noteq> 0` and `\<bar>x\<bar> < ?s n` show "\<bar>?diff n x - f' x0 n\<bar> < ?r"
```
```   785         by blast
```
```   786     qed auto
```
```   787     also have "\<dots> = of_nat (card {0 ..< ?N}) * ?r"
```
```   788       by (rule setsum_constant)
```
```   789     also have "\<dots> = real ?N * ?r"
```
```   790       unfolding real_eq_of_nat by auto
```
```   791     also have "\<dots> = r/3" by auto
```
```   792     finally have "\<bar>\<Sum>n \<in> { 0 ..< ?N}. ?diff n x - f' x0 n \<bar> < r / 3" (is "?diff_part < r / 3") .
```
```   793
```
```   794     from suminf_diff[OF allf_summable[OF x_in_I] allf_summable[OF x0_in_I]]
```
```   795     have "\<bar>(suminf (f (x0 + x)) - (suminf (f x0))) / x - suminf (f' x0)\<bar> =
```
```   796         \<bar>\<Sum>n. ?diff n x - f' x0 n\<bar>"
```
```   797       unfolding suminf_diff[OF div_smbl `summable (f' x0)`, symmetric]
```
```   798       using suminf_divide[OF diff_smbl, symmetric] by auto
```
```   799     also have "\<dots> \<le> ?diff_part + \<bar> (\<Sum>n. ?diff (n + ?N) x) - (\<Sum> n. f' x0 (n + ?N)) \<bar>"
```
```   800       unfolding suminf_split_initial_segment[OF all_smbl, where k="?N"]
```
```   801       unfolding suminf_diff[OF div_shft_smbl ign[OF `summable (f' x0)`]]
```
```   802       by (rule abs_triangle_ineq)
```
```   803     also have "\<dots> \<le> ?diff_part + ?L_part + ?f'_part"
```
```   804       using abs_triangle_ineq4 by auto
```
```   805     also have "\<dots> < r /3 + r/3 + r/3"
```
```   806       using `?diff_part < r/3` `?L_part \<le> r/3` and `?f'_part < r/3`
```
```   807       by (rule add_strict_mono [OF add_less_le_mono])
```
```   808     finally have "\<bar>(suminf (f (x0 + x)) - suminf (f x0)) / x - suminf (f' x0)\<bar> < r"
```
```   809       by auto
```
```   810   }
```
```   811   thus "\<exists> s > 0. \<forall> x. x \<noteq> 0 \<and> norm (x - 0) < s \<longrightarrow>
```
```   812       norm (((\<Sum>n. f (x0 + x) n) - (\<Sum>n. f x0 n)) / x - (\<Sum>n. f' x0 n)) < r"
```
```   813     using `0 < S` unfolding real_norm_def diff_0_right by blast
```
```   814 qed
```
```   815
```
```   816 lemma DERIV_power_series':
```
```   817   fixes f :: "nat \<Rightarrow> real"
```
```   818   assumes converges: "\<And> x. x \<in> {-R <..< R} \<Longrightarrow> summable (\<lambda> n. f n * real (Suc n) * x^n)"
```
```   819     and x0_in_I: "x0 \<in> {-R <..< R}" and "0 < R"
```
```   820   shows "DERIV (\<lambda> x. (\<Sum> n. f n * x^(Suc n))) x0 :> (\<Sum> n. f n * real (Suc n) * x0^n)"
```
```   821   (is "DERIV (\<lambda> x. (suminf (?f x))) x0 :> (suminf (?f' x0))")
```
```   822 proof -
```
```   823   {
```
```   824     fix R'
```
```   825     assume "0 < R'" and "R' < R" and "-R' < x0" and "x0 < R'"
```
```   826     hence "x0 \<in> {-R' <..< R'}" and "R' \<in> {-R <..< R}" and "x0 \<in> {-R <..< R}"
```
```   827       by auto
```
```   828     have "DERIV (\<lambda> x. (suminf (?f x))) x0 :> (suminf (?f' x0))"
```
```   829     proof (rule DERIV_series')
```
```   830       show "summable (\<lambda> n. \<bar>f n * real (Suc n) * R'^n\<bar>)"
```
```   831       proof -
```
```   832         have "(R' + R) / 2 < R" and "0 < (R' + R) / 2"
```
```   833           using `0 < R'` `0 < R` `R' < R` by auto
```
```   834         hence in_Rball: "(R' + R) / 2 \<in> {-R <..< R}"
```
```   835           using `R' < R` by auto
```
```   836         have "norm R' < norm ((R' + R) / 2)"
```
```   837           using `0 < R'` `0 < R` `R' < R` by auto
```
```   838         from powser_insidea[OF converges[OF in_Rball] this] show ?thesis
```
```   839           by auto
```
```   840       qed
```
```   841       {
```
```   842         fix n x y
```
```   843         assume "x \<in> {-R' <..< R'}" and "y \<in> {-R' <..< R'}"
```
```   844         show "\<bar>?f x n - ?f y n\<bar> \<le> \<bar>f n * real (Suc n) * R'^n\<bar> * \<bar>x-y\<bar>"
```
```   845         proof -
```
```   846           have "\<bar>f n * x ^ (Suc n) - f n * y ^ (Suc n)\<bar> =
```
```   847             (\<bar>f n\<bar> * \<bar>x-y\<bar>) * \<bar>\<Sum>p = 0..<Suc n. x ^ p * y ^ (n - p)\<bar>"
```
```   848             unfolding right_diff_distrib[symmetric] lemma_realpow_diff_sumr2 abs_mult
```
```   849             by auto
```
```   850           also have "\<dots> \<le> (\<bar>f n\<bar> * \<bar>x-y\<bar>) * (\<bar>real (Suc n)\<bar> * \<bar>R' ^ n\<bar>)"
```
```   851           proof (rule mult_left_mono)
```
```   852             have "\<bar>\<Sum>p = 0..<Suc n. x ^ p * y ^ (n - p)\<bar> \<le> (\<Sum>p = 0..<Suc n. \<bar>x ^ p * y ^ (n - p)\<bar>)"
```
```   853               by (rule setsum_abs)
```
```   854             also have "\<dots> \<le> (\<Sum>p = 0..<Suc n. R' ^ n)"
```
```   855             proof (rule setsum_mono)
```
```   856               fix p
```
```   857               assume "p \<in> {0..<Suc n}"
```
```   858               hence "p \<le> n" by auto
```
```   859               {
```
```   860                 fix n
```
```   861                 fix x :: real
```
```   862                 assume "x \<in> {-R'<..<R'}"
```
```   863                 hence "\<bar>x\<bar> \<le> R'"  by auto
```
```   864                 hence "\<bar>x^n\<bar> \<le> R'^n"
```
```   865                   unfolding power_abs by (rule power_mono, auto)
```
```   866               }
```
```   867               from mult_mono[OF this[OF `x \<in> {-R'<..<R'}`, of p] this[OF `y \<in> {-R'<..<R'}`, of "n-p"]] `0 < R'`
```
```   868               have "\<bar>x^p * y^(n-p)\<bar> \<le> R'^p * R'^(n-p)"
```
```   869                 unfolding abs_mult by auto
```
```   870               thus "\<bar>x^p * y^(n-p)\<bar> \<le> R'^n"
```
```   871                 unfolding power_add[symmetric] using `p \<le> n` by auto
```
```   872             qed
```
```   873             also have "\<dots> = real (Suc n) * R' ^ n"
```
```   874               unfolding setsum_constant card_atLeastLessThan real_of_nat_def by auto
```
```   875             finally show "\<bar>\<Sum>p = 0..<Suc n. x ^ p * y ^ (n - p)\<bar> \<le> \<bar>real (Suc n)\<bar> * \<bar>R' ^ n\<bar>"
```
```   876               unfolding abs_real_of_nat_cancel abs_of_nonneg[OF zero_le_power[OF less_imp_le[OF `0 < R'`]]] .
```
```   877             show "0 \<le> \<bar>f n\<bar> * \<bar>x - y\<bar>"
```
```   878               unfolding abs_mult[symmetric] by auto
```
```   879           qed
```
```   880           also have "\<dots> = \<bar>f n * real (Suc n) * R' ^ n\<bar> * \<bar>x - y\<bar>"
```
```   881             unfolding abs_mult mult_assoc[symmetric] by algebra
```
```   882           finally show ?thesis .
```
```   883         qed
```
```   884       }
```
```   885       {
```
```   886         fix n
```
```   887         show "DERIV (\<lambda> x. ?f x n) x0 :> (?f' x0 n)"
```
```   888           by (auto intro!: DERIV_intros simp del: power_Suc)
```
```   889       }
```
```   890       {
```
```   891         fix x
```
```   892         assume "x \<in> {-R' <..< R'}"
```
```   893         hence "R' \<in> {-R <..< R}" and "norm x < norm R'"
```
```   894           using assms `R' < R` by auto
```
```   895         have "summable (\<lambda> n. f n * x^n)"
```
```   896         proof (rule summable_le2[THEN conjunct1, OF _ powser_insidea[OF converges[OF `R' \<in> {-R <..< R}`] `norm x < norm R'`]], rule allI)
```
```   897           fix n
```
```   898           have le: "\<bar>f n\<bar> * 1 \<le> \<bar>f n\<bar> * real (Suc n)"
```
```   899             by (rule mult_left_mono) auto
```
```   900           show "\<bar>f n * x ^ n\<bar> \<le> norm (f n * real (Suc n) * x ^ n)"
```
```   901             unfolding real_norm_def abs_mult
```
```   902             by (rule mult_right_mono) (auto simp add: le[unfolded mult_1_right])
```
```   903         qed
```
```   904         from this[THEN summable_mult2[where c=x], unfolded mult_assoc, unfolded mult_commute]
```
```   905         show "summable (?f x)" by auto
```
```   906       }
```
```   907       show "summable (?f' x0)"
```
```   908         using converges[OF `x0 \<in> {-R <..< R}`] .
```
```   909       show "x0 \<in> {-R' <..< R'}"
```
```   910         using `x0 \<in> {-R' <..< R'}` .
```
```   911     qed
```
```   912   } note for_subinterval = this
```
```   913   let ?R = "(R + \<bar>x0\<bar>) / 2"
```
```   914   have "\<bar>x0\<bar> < ?R" using assms by auto
```
```   915   hence "- ?R < x0"
```
```   916   proof (cases "x0 < 0")
```
```   917     case True
```
```   918     hence "- x0 < ?R" using `\<bar>x0\<bar> < ?R` by auto
```
```   919     thus ?thesis unfolding neg_less_iff_less[symmetric, of "- x0"] by auto
```
```   920   next
```
```   921     case False
```
```   922     have "- ?R < 0" using assms by auto
```
```   923     also have "\<dots> \<le> x0" using False by auto
```
```   924     finally show ?thesis .
```
```   925   qed
```
```   926   hence "0 < ?R" "?R < R" "- ?R < x0" and "x0 < ?R"
```
```   927     using assms by auto
```
```   928   from for_subinterval[OF this]
```
```   929   show ?thesis .
```
```   930 qed
```
```   931
```
```   932
```
```   933 subsection {* Exponential Function *}
```
```   934
```
```   935 definition exp :: "'a \<Rightarrow> 'a::{real_normed_field,banach}"
```
```   936   where "exp = (\<lambda>x. \<Sum>n. x ^ n /\<^sub>R real (fact n))"
```
```   937
```
```   938 lemma summable_exp_generic:
```
```   939   fixes x :: "'a::{real_normed_algebra_1,banach}"
```
```   940   defines S_def: "S \<equiv> \<lambda>n. x ^ n /\<^sub>R real (fact n)"
```
```   941   shows "summable S"
```
```   942 proof -
```
```   943   have S_Suc: "\<And>n. S (Suc n) = (x * S n) /\<^sub>R real (Suc n)"
```
```   944     unfolding S_def by (simp del: mult_Suc)
```
```   945   obtain r :: real where r0: "0 < r" and r1: "r < 1"
```
```   946     using dense [OF zero_less_one] by fast
```
```   947   obtain N :: nat where N: "norm x < real N * r"
```
```   948     using reals_Archimedean3 [OF r0] by fast
```
```   949   from r1 show ?thesis
```
```   950   proof (rule ratio_test [rule_format])
```
```   951     fix n :: nat
```
```   952     assume n: "N \<le> n"
```
```   953     have "norm x \<le> real N * r"
```
```   954       using N by (rule order_less_imp_le)
```
```   955     also have "real N * r \<le> real (Suc n) * r"
```
```   956       using r0 n by (simp add: mult_right_mono)
```
```   957     finally have "norm x * norm (S n) \<le> real (Suc n) * r * norm (S n)"
```
```   958       using norm_ge_zero by (rule mult_right_mono)
```
```   959     hence "norm (x * S n) \<le> real (Suc n) * r * norm (S n)"
```
```   960       by (rule order_trans [OF norm_mult_ineq])
```
```   961     hence "norm (x * S n) / real (Suc n) \<le> r * norm (S n)"
```
```   962       by (simp add: pos_divide_le_eq mult_ac)
```
```   963     thus "norm (S (Suc n)) \<le> r * norm (S n)"
```
```   964       by (simp add: S_Suc inverse_eq_divide)
```
```   965   qed
```
```   966 qed
```
```   967
```
```   968 lemma summable_norm_exp:
```
```   969   fixes x :: "'a::{real_normed_algebra_1,banach}"
```
```   970   shows "summable (\<lambda>n. norm (x ^ n /\<^sub>R real (fact n)))"
```
```   971 proof (rule summable_norm_comparison_test [OF exI, rule_format])
```
```   972   show "summable (\<lambda>n. norm x ^ n /\<^sub>R real (fact n))"
```
```   973     by (rule summable_exp_generic)
```
```   974   fix n
```
```   975   show "norm (x ^ n /\<^sub>R real (fact n)) \<le> norm x ^ n /\<^sub>R real (fact n)"
```
```   976     by (simp add: norm_power_ineq)
```
```   977 qed
```
```   978
```
```   979 lemma summable_exp: "summable (\<lambda>n. inverse (real (fact n)) * x ^ n)"
```
```   980   using summable_exp_generic [where x=x] by simp
```
```   981
```
```   982 lemma exp_converges: "(\<lambda>n. x ^ n /\<^sub>R real (fact n)) sums exp x"
```
```   983   unfolding exp_def by (rule summable_exp_generic [THEN summable_sums])
```
```   984
```
```   985
```
```   986 lemma exp_fdiffs:
```
```   987       "diffs (\<lambda>n. inverse(real (fact n))) = (\<lambda>n. inverse(real (fact n)))"
```
```   988   by (simp add: diffs_def mult_assoc [symmetric] real_of_nat_def of_nat_mult
```
```   989         del: mult_Suc of_nat_Suc)
```
```   990
```
```   991 lemma diffs_of_real: "diffs (\<lambda>n. of_real (f n)) = (\<lambda>n. of_real (diffs f n))"
```
```   992   by (simp add: diffs_def)
```
```   993
```
```   994 lemma DERIV_exp [simp]: "DERIV exp x :> exp(x)"
```
```   995   unfolding exp_def scaleR_conv_of_real
```
```   996   apply (rule DERIV_cong)
```
```   997   apply (rule termdiffs [where K="of_real (1 + norm x)"])
```
```   998   apply (simp_all only: diffs_of_real scaleR_conv_of_real exp_fdiffs)
```
```   999   apply (rule exp_converges [THEN sums_summable, unfolded scaleR_conv_of_real])+
```
```  1000   apply (simp del: of_real_add)
```
```  1001   done
```
```  1002
```
```  1003 declare DERIV_exp[THEN DERIV_chain2, THEN DERIV_cong, DERIV_intros]
```
```  1004
```
```  1005 lemma isCont_exp: "isCont exp x"
```
```  1006   by (rule DERIV_exp [THEN DERIV_isCont])
```
```  1007
```
```  1008 lemma isCont_exp' [simp]: "isCont f a \<Longrightarrow> isCont (\<lambda>x. exp (f x)) a"
```
```  1009   by (rule isCont_o2 [OF _ isCont_exp])
```
```  1010
```
```  1011 lemma tendsto_exp [tendsto_intros]:
```
```  1012   "(f ---> a) F \<Longrightarrow> ((\<lambda>x. exp (f x)) ---> exp a) F"
```
```  1013   by (rule isCont_tendsto_compose [OF isCont_exp])
```
```  1014
```
```  1015 lemma continuous_exp [continuous_intros]:
```
```  1016   "continuous F f \<Longrightarrow> continuous F (\<lambda>x. exp (f x))"
```
```  1017   unfolding continuous_def by (rule tendsto_exp)
```
```  1018
```
```  1019 lemma continuous_on_exp [continuous_on_intros]:
```
```  1020   "continuous_on s f \<Longrightarrow> continuous_on s (\<lambda>x. exp (f x))"
```
```  1021   unfolding continuous_on_def by (auto intro: tendsto_exp)
```
```  1022
```
```  1023
```
```  1024 subsubsection {* Properties of the Exponential Function *}
```
```  1025
```
```  1026 lemma powser_zero:
```
```  1027   fixes f :: "nat \<Rightarrow> 'a::{real_normed_algebra_1}"
```
```  1028   shows "(\<Sum>n. f n * 0 ^ n) = f 0"
```
```  1029 proof -
```
```  1030   have "(\<Sum>n = 0..<1. f n * 0 ^ n) = (\<Sum>n. f n * 0 ^ n)"
```
```  1031     by (rule sums_unique [OF series_zero], simp add: power_0_left)
```
```  1032   thus ?thesis unfolding One_nat_def by simp
```
```  1033 qed
```
```  1034
```
```  1035 lemma exp_zero [simp]: "exp 0 = 1"
```
```  1036   unfolding exp_def by (simp add: scaleR_conv_of_real powser_zero)
```
```  1037
```
```  1038 lemma setsum_cl_ivl_Suc2:
```
```  1039   "(\<Sum>i=m..Suc n. f i) = (if Suc n < m then 0 else f m + (\<Sum>i=m..n. f (Suc i)))"
```
```  1040   by (simp add: setsum_head_Suc setsum_shift_bounds_cl_Suc_ivl
```
```  1041            del: setsum_cl_ivl_Suc)
```
```  1042
```
```  1043 lemma exp_series_add:
```
```  1044   fixes x y :: "'a::{real_field}"
```
```  1045   defines S_def: "S \<equiv> \<lambda>x n. x ^ n /\<^sub>R real (fact n)"
```
```  1046   shows "S (x + y) n = (\<Sum>i=0..n. S x i * S y (n - i))"
```
```  1047 proof (induct n)
```
```  1048   case 0
```
```  1049   show ?case
```
```  1050     unfolding S_def by simp
```
```  1051 next
```
```  1052   case (Suc n)
```
```  1053   have S_Suc: "\<And>x n. S x (Suc n) = (x * S x n) /\<^sub>R real (Suc n)"
```
```  1054     unfolding S_def by (simp del: mult_Suc)
```
```  1055   hence times_S: "\<And>x n. x * S x n = real (Suc n) *\<^sub>R S x (Suc n)"
```
```  1056     by simp
```
```  1057
```
```  1058   have "real (Suc n) *\<^sub>R S (x + y) (Suc n) = (x + y) * S (x + y) n"
```
```  1059     by (simp only: times_S)
```
```  1060   also have "\<dots> = (x + y) * (\<Sum>i=0..n. S x i * S y (n-i))"
```
```  1061     by (simp only: Suc)
```
```  1062   also have "\<dots> = x * (\<Sum>i=0..n. S x i * S y (n-i))
```
```  1063                 + y * (\<Sum>i=0..n. S x i * S y (n-i))"
```
```  1064     by (rule distrib_right)
```
```  1065   also have "\<dots> = (\<Sum>i=0..n. (x * S x i) * S y (n-i))
```
```  1066                 + (\<Sum>i=0..n. S x i * (y * S y (n-i)))"
```
```  1067     by (simp only: setsum_right_distrib mult_ac)
```
```  1068   also have "\<dots> = (\<Sum>i=0..n. real (Suc i) *\<^sub>R (S x (Suc i) * S y (n-i)))
```
```  1069                 + (\<Sum>i=0..n. real (Suc n-i) *\<^sub>R (S x i * S y (Suc n-i)))"
```
```  1070     by (simp add: times_S Suc_diff_le)
```
```  1071   also have "(\<Sum>i=0..n. real (Suc i) *\<^sub>R (S x (Suc i) * S y (n-i))) =
```
```  1072              (\<Sum>i=0..Suc n. real i *\<^sub>R (S x i * S y (Suc n-i)))"
```
```  1073     by (subst setsum_cl_ivl_Suc2, simp)
```
```  1074   also have "(\<Sum>i=0..n. real (Suc n-i) *\<^sub>R (S x i * S y (Suc n-i))) =
```
```  1075              (\<Sum>i=0..Suc n. real (Suc n-i) *\<^sub>R (S x i * S y (Suc n-i)))"
```
```  1076     by (subst setsum_cl_ivl_Suc, simp)
```
```  1077   also have "(\<Sum>i=0..Suc n. real i *\<^sub>R (S x i * S y (Suc n-i))) +
```
```  1078              (\<Sum>i=0..Suc n. real (Suc n-i) *\<^sub>R (S x i * S y (Suc n-i))) =
```
```  1079              (\<Sum>i=0..Suc n. real (Suc n) *\<^sub>R (S x i * S y (Suc n-i)))"
```
```  1080     by (simp only: setsum_addf [symmetric] scaleR_left_distrib [symmetric]
```
```  1081               real_of_nat_add [symmetric], simp)
```
```  1082   also have "\<dots> = real (Suc n) *\<^sub>R (\<Sum>i=0..Suc n. S x i * S y (Suc n-i))"
```
```  1083     by (simp only: scaleR_right.setsum)
```
```  1084   finally show
```
```  1085     "S (x + y) (Suc n) = (\<Sum>i=0..Suc n. S x i * S y (Suc n - i))"
```
```  1086     by (simp del: setsum_cl_ivl_Suc)
```
```  1087 qed
```
```  1088
```
```  1089 lemma exp_add: "exp (x + y) = exp x * exp y"
```
```  1090   unfolding exp_def
```
```  1091   by (simp only: Cauchy_product summable_norm_exp exp_series_add)
```
```  1092
```
```  1093 lemma mult_exp_exp: "exp x * exp y = exp (x + y)"
```
```  1094   by (rule exp_add [symmetric])
```
```  1095
```
```  1096 lemma exp_of_real: "exp (of_real x) = of_real (exp x)"
```
```  1097   unfolding exp_def
```
```  1098   apply (subst suminf_of_real)
```
```  1099   apply (rule summable_exp_generic)
```
```  1100   apply (simp add: scaleR_conv_of_real)
```
```  1101   done
```
```  1102
```
```  1103 lemma exp_not_eq_zero [simp]: "exp x \<noteq> 0"
```
```  1104 proof
```
```  1105   have "exp x * exp (- x) = 1" by (simp add: mult_exp_exp)
```
```  1106   also assume "exp x = 0"
```
```  1107   finally show "False" by simp
```
```  1108 qed
```
```  1109
```
```  1110 lemma exp_minus: "exp (- x) = inverse (exp x)"
```
```  1111   by (rule inverse_unique [symmetric], simp add: mult_exp_exp)
```
```  1112
```
```  1113 lemma exp_diff: "exp (x - y) = exp x / exp y"
```
```  1114   using exp_add [of x "- y"] by (simp add: exp_minus divide_inverse)
```
```  1115
```
```  1116
```
```  1117 subsubsection {* Properties of the Exponential Function on Reals *}
```
```  1118
```
```  1119 text {* Comparisons of @{term "exp x"} with zero. *}
```
```  1120
```
```  1121 text{*Proof: because every exponential can be seen as a square.*}
```
```  1122 lemma exp_ge_zero [simp]: "0 \<le> exp (x::real)"
```
```  1123 proof -
```
```  1124   have "0 \<le> exp (x/2) * exp (x/2)" by simp
```
```  1125   thus ?thesis by (simp add: exp_add [symmetric])
```
```  1126 qed
```
```  1127
```
```  1128 lemma exp_gt_zero [simp]: "0 < exp (x::real)"
```
```  1129   by (simp add: order_less_le)
```
```  1130
```
```  1131 lemma not_exp_less_zero [simp]: "\<not> exp (x::real) < 0"
```
```  1132   by (simp add: not_less)
```
```  1133
```
```  1134 lemma not_exp_le_zero [simp]: "\<not> exp (x::real) \<le> 0"
```
```  1135   by (simp add: not_le)
```
```  1136
```
```  1137 lemma abs_exp_cancel [simp]: "\<bar>exp x::real\<bar> = exp x"
```
```  1138   by simp
```
```  1139
```
```  1140 lemma exp_real_of_nat_mult: "exp(real n * x) = exp(x) ^ n"
```
```  1141   by (induct n) (auto simp add: real_of_nat_Suc distrib_left exp_add mult_commute)
```
```  1142
```
```  1143 text {* Strict monotonicity of exponential. *}
```
```  1144
```
```  1145 lemma exp_ge_add_one_self_aux:
```
```  1146   assumes "0 \<le> (x::real)" shows "1+x \<le> exp(x)"
```
```  1147 using order_le_imp_less_or_eq [OF assms]
```
```  1148 proof
```
```  1149   assume "0 < x"
```
```  1150   have "1+x \<le> (\<Sum>n = 0..<2. inverse (real (fact n)) * x ^ n)"
```
```  1151     by (auto simp add: numeral_2_eq_2)
```
```  1152   also have "... \<le> (\<Sum>n. inverse (real (fact n)) * x ^ n)"
```
```  1153     apply (rule series_pos_le [OF summable_exp])
```
```  1154     using `0 < x`
```
```  1155     apply (auto  simp add:  zero_le_mult_iff)
```
```  1156     done
```
```  1157   finally show "1+x \<le> exp x"
```
```  1158     by (simp add: exp_def)
```
```  1159 next
```
```  1160   assume "0 = x"
```
```  1161   then show "1 + x \<le> exp x"
```
```  1162     by auto
```
```  1163 qed
```
```  1164
```
```  1165 lemma exp_gt_one: "0 < (x::real) \<Longrightarrow> 1 < exp x"
```
```  1166 proof -
```
```  1167   assume x: "0 < x"
```
```  1168   hence "1 < 1 + x" by simp
```
```  1169   also from x have "1 + x \<le> exp x"
```
```  1170     by (simp add: exp_ge_add_one_self_aux)
```
```  1171   finally show ?thesis .
```
```  1172 qed
```
```  1173
```
```  1174 lemma exp_less_mono:
```
```  1175   fixes x y :: real
```
```  1176   assumes "x < y"
```
```  1177   shows "exp x < exp y"
```
```  1178 proof -
```
```  1179   from `x < y` have "0 < y - x" by simp
```
```  1180   hence "1 < exp (y - x)" by (rule exp_gt_one)
```
```  1181   hence "1 < exp y / exp x" by (simp only: exp_diff)
```
```  1182   thus "exp x < exp y" by simp
```
```  1183 qed
```
```  1184
```
```  1185 lemma exp_less_cancel: "exp (x::real) < exp y \<Longrightarrow> x < y"
```
```  1186   unfolding linorder_not_le [symmetric]
```
```  1187   by (auto simp add: order_le_less exp_less_mono)
```
```  1188
```
```  1189 lemma exp_less_cancel_iff [iff]: "exp (x::real) < exp y \<longleftrightarrow> x < y"
```
```  1190   by (auto intro: exp_less_mono exp_less_cancel)
```
```  1191
```
```  1192 lemma exp_le_cancel_iff [iff]: "exp (x::real) \<le> exp y \<longleftrightarrow> x \<le> y"
```
```  1193   by (auto simp add: linorder_not_less [symmetric])
```
```  1194
```
```  1195 lemma exp_inj_iff [iff]: "exp (x::real) = exp y \<longleftrightarrow> x = y"
```
```  1196   by (simp add: order_eq_iff)
```
```  1197
```
```  1198 text {* Comparisons of @{term "exp x"} with one. *}
```
```  1199
```
```  1200 lemma one_less_exp_iff [simp]: "1 < exp (x::real) \<longleftrightarrow> 0 < x"
```
```  1201   using exp_less_cancel_iff [where x=0 and y=x] by simp
```
```  1202
```
```  1203 lemma exp_less_one_iff [simp]: "exp (x::real) < 1 \<longleftrightarrow> x < 0"
```
```  1204   using exp_less_cancel_iff [where x=x and y=0] by simp
```
```  1205
```
```  1206 lemma one_le_exp_iff [simp]: "1 \<le> exp (x::real) \<longleftrightarrow> 0 \<le> x"
```
```  1207   using exp_le_cancel_iff [where x=0 and y=x] by simp
```
```  1208
```
```  1209 lemma exp_le_one_iff [simp]: "exp (x::real) \<le> 1 \<longleftrightarrow> x \<le> 0"
```
```  1210   using exp_le_cancel_iff [where x=x and y=0] by simp
```
```  1211
```
```  1212 lemma exp_eq_one_iff [simp]: "exp (x::real) = 1 \<longleftrightarrow> x = 0"
```
```  1213   using exp_inj_iff [where x=x and y=0] by simp
```
```  1214
```
```  1215 lemma lemma_exp_total: "1 \<le> y \<Longrightarrow> \<exists>x. 0 \<le> x & x \<le> y - 1 & exp(x::real) = y"
```
```  1216 proof (rule IVT)
```
```  1217   assume "1 \<le> y"
```
```  1218   hence "0 \<le> y - 1" by simp
```
```  1219   hence "1 + (y - 1) \<le> exp (y - 1)" by (rule exp_ge_add_one_self_aux)
```
```  1220   thus "y \<le> exp (y - 1)" by simp
```
```  1221 qed (simp_all add: le_diff_eq)
```
```  1222
```
```  1223 lemma exp_total: "0 < (y::real) \<Longrightarrow> \<exists>x. exp x = y"
```
```  1224 proof (rule linorder_le_cases [of 1 y])
```
```  1225   assume "1 \<le> y"
```
```  1226   thus "\<exists>x. exp x = y" by (fast dest: lemma_exp_total)
```
```  1227 next
```
```  1228   assume "0 < y" and "y \<le> 1"
```
```  1229   hence "1 \<le> inverse y" by (simp add: one_le_inverse_iff)
```
```  1230   then obtain x where "exp x = inverse y" by (fast dest: lemma_exp_total)
```
```  1231   hence "exp (- x) = y" by (simp add: exp_minus)
```
```  1232   thus "\<exists>x. exp x = y" ..
```
```  1233 qed
```
```  1234
```
```  1235
```
```  1236 subsection {* Natural Logarithm *}
```
```  1237
```
```  1238 definition ln :: "real \<Rightarrow> real"
```
```  1239   where "ln x = (THE u. exp u = x)"
```
```  1240
```
```  1241 lemma ln_exp [simp]: "ln (exp x) = x"
```
```  1242   by (simp add: ln_def)
```
```  1243
```
```  1244 lemma exp_ln [simp]: "0 < x \<Longrightarrow> exp (ln x) = x"
```
```  1245   by (auto dest: exp_total)
```
```  1246
```
```  1247 lemma exp_ln_iff [simp]: "exp (ln x) = x \<longleftrightarrow> 0 < x"
```
```  1248   by (metis exp_gt_zero exp_ln)
```
```  1249
```
```  1250 lemma ln_unique: "exp y = x \<Longrightarrow> ln x = y"
```
```  1251   by (erule subst, rule ln_exp)
```
```  1252
```
```  1253 lemma ln_one [simp]: "ln 1 = 0"
```
```  1254   by (rule ln_unique) simp
```
```  1255
```
```  1256 lemma ln_mult: "0 < x \<Longrightarrow> 0 < y \<Longrightarrow> ln (x * y) = ln x + ln y"
```
```  1257   by (rule ln_unique) (simp add: exp_add)
```
```  1258
```
```  1259 lemma ln_inverse: "0 < x \<Longrightarrow> ln (inverse x) = - ln x"
```
```  1260   by (rule ln_unique) (simp add: exp_minus)
```
```  1261
```
```  1262 lemma ln_div: "0 < x \<Longrightarrow> 0 < y \<Longrightarrow> ln (x / y) = ln x - ln y"
```
```  1263   by (rule ln_unique) (simp add: exp_diff)
```
```  1264
```
```  1265 lemma ln_realpow: "0 < x \<Longrightarrow> ln (x ^ n) = real n * ln x"
```
```  1266   by (rule ln_unique) (simp add: exp_real_of_nat_mult)
```
```  1267
```
```  1268 lemma ln_less_cancel_iff [simp]: "0 < x \<Longrightarrow> 0 < y \<Longrightarrow> ln x < ln y \<longleftrightarrow> x < y"
```
```  1269   by (subst exp_less_cancel_iff [symmetric]) simp
```
```  1270
```
```  1271 lemma ln_le_cancel_iff [simp]: "0 < x \<Longrightarrow> 0 < y \<Longrightarrow> ln x \<le> ln y \<longleftrightarrow> x \<le> y"
```
```  1272   by (simp add: linorder_not_less [symmetric])
```
```  1273
```
```  1274 lemma ln_inj_iff [simp]: "0 < x \<Longrightarrow> 0 < y \<Longrightarrow> ln x = ln y \<longleftrightarrow> x = y"
```
```  1275   by (simp add: order_eq_iff)
```
```  1276
```
```  1277 lemma ln_add_one_self_le_self [simp]: "0 \<le> x \<Longrightarrow> ln (1 + x) \<le> x"
```
```  1278   apply (rule exp_le_cancel_iff [THEN iffD1])
```
```  1279   apply (simp add: exp_ge_add_one_self_aux)
```
```  1280   done
```
```  1281
```
```  1282 lemma ln_less_self [simp]: "0 < x \<Longrightarrow> ln x < x"
```
```  1283   by (rule order_less_le_trans [where y="ln (1 + x)"]) simp_all
```
```  1284
```
```  1285 lemma ln_ge_zero [simp]: "1 \<le> x \<Longrightarrow> 0 \<le> ln x"
```
```  1286   using ln_le_cancel_iff [of 1 x] by simp
```
```  1287
```
```  1288 lemma ln_ge_zero_imp_ge_one: "0 \<le> ln x \<Longrightarrow> 0 < x \<Longrightarrow> 1 \<le> x"
```
```  1289   using ln_le_cancel_iff [of 1 x] by simp
```
```  1290
```
```  1291 lemma ln_ge_zero_iff [simp]: "0 < x \<Longrightarrow> 0 \<le> ln x \<longleftrightarrow> 1 \<le> x"
```
```  1292   using ln_le_cancel_iff [of 1 x] by simp
```
```  1293
```
```  1294 lemma ln_less_zero_iff [simp]: "0 < x \<Longrightarrow> ln x < 0 \<longleftrightarrow> x < 1"
```
```  1295   using ln_less_cancel_iff [of x 1] by simp
```
```  1296
```
```  1297 lemma ln_gt_zero: "1 < x \<Longrightarrow> 0 < ln x"
```
```  1298   using ln_less_cancel_iff [of 1 x] by simp
```
```  1299
```
```  1300 lemma ln_gt_zero_imp_gt_one: "0 < ln x \<Longrightarrow> 0 < x \<Longrightarrow> 1 < x"
```
```  1301   using ln_less_cancel_iff [of 1 x] by simp
```
```  1302
```
```  1303 lemma ln_gt_zero_iff [simp]: "0 < x \<Longrightarrow> 0 < ln x \<longleftrightarrow> 1 < x"
```
```  1304   using ln_less_cancel_iff [of 1 x] by simp
```
```  1305
```
```  1306 lemma ln_eq_zero_iff [simp]: "0 < x \<Longrightarrow> ln x = 0 \<longleftrightarrow> x = 1"
```
```  1307   using ln_inj_iff [of x 1] by simp
```
```  1308
```
```  1309 lemma ln_less_zero: "0 < x \<Longrightarrow> x < 1 \<Longrightarrow> ln x < 0"
```
```  1310   by simp
```
```  1311
```
```  1312 lemma isCont_ln: "0 < x \<Longrightarrow> isCont ln x"
```
```  1313   apply (subgoal_tac "isCont ln (exp (ln x))", simp)
```
```  1314   apply (rule isCont_inverse_function [where f=exp], simp_all)
```
```  1315   done
```
```  1316
```
```  1317 lemma tendsto_ln [tendsto_intros]:
```
```  1318   "(f ---> a) F \<Longrightarrow> 0 < a \<Longrightarrow> ((\<lambda>x. ln (f x)) ---> ln a) F"
```
```  1319   by (rule isCont_tendsto_compose [OF isCont_ln])
```
```  1320
```
```  1321 lemma continuous_ln:
```
```  1322   "continuous F f \<Longrightarrow> 0 < f (Lim F (\<lambda>x. x)) \<Longrightarrow> continuous F (\<lambda>x. ln (f x))"
```
```  1323   unfolding continuous_def by (rule tendsto_ln)
```
```  1324
```
```  1325 lemma isCont_ln' [continuous_intros]:
```
```  1326   "continuous (at x) f \<Longrightarrow> 0 < f x \<Longrightarrow> continuous (at x) (\<lambda>x. ln (f x))"
```
```  1327   unfolding continuous_at by (rule tendsto_ln)
```
```  1328
```
```  1329 lemma continuous_within_ln [continuous_intros]:
```
```  1330   "continuous (at x within s) f \<Longrightarrow> 0 < f x \<Longrightarrow> continuous (at x within s) (\<lambda>x. ln (f x))"
```
```  1331   unfolding continuous_within by (rule tendsto_ln)
```
```  1332
```
```  1333 lemma continuous_on_ln [continuous_on_intros]:
```
```  1334   "continuous_on s f \<Longrightarrow> (\<forall>x\<in>s. 0 < f x) \<Longrightarrow> continuous_on s (\<lambda>x. ln (f x))"
```
```  1335   unfolding continuous_on_def by (auto intro: tendsto_ln)
```
```  1336
```
```  1337 lemma DERIV_ln: "0 < x \<Longrightarrow> DERIV ln x :> inverse x"
```
```  1338   apply (rule DERIV_inverse_function [where f=exp and a=0 and b="x+1"])
```
```  1339   apply (auto intro: DERIV_cong [OF DERIV_exp exp_ln] isCont_ln)
```
```  1340   done
```
```  1341
```
```  1342 lemma DERIV_ln_divide: "0 < x \<Longrightarrow> DERIV ln x :> 1 / x"
```
```  1343   by (rule DERIV_ln[THEN DERIV_cong], simp, simp add: divide_inverse)
```
```  1344
```
```  1345 declare DERIV_ln_divide[THEN DERIV_chain2, THEN DERIV_cong, DERIV_intros]
```
```  1346
```
```  1347 lemma ln_series:
```
```  1348   assumes "0 < x" and "x < 2"
```
```  1349   shows "ln x = (\<Sum> n. (-1)^n * (1 / real (n + 1)) * (x - 1)^(Suc n))"
```
```  1350   (is "ln x = suminf (?f (x - 1))")
```
```  1351 proof -
```
```  1352   let ?f' = "\<lambda>x n. (-1)^n * (x - 1)^n"
```
```  1353
```
```  1354   have "ln x - suminf (?f (x - 1)) = ln 1 - suminf (?f (1 - 1))"
```
```  1355   proof (rule DERIV_isconst3[where x=x])
```
```  1356     fix x :: real
```
```  1357     assume "x \<in> {0 <..< 2}"
```
```  1358     hence "0 < x" and "x < 2" by auto
```
```  1359     have "norm (1 - x) < 1"
```
```  1360       using `0 < x` and `x < 2` by auto
```
```  1361     have "1 / x = 1 / (1 - (1 - x))" by auto
```
```  1362     also have "\<dots> = (\<Sum> n. (1 - x)^n)"
```
```  1363       using geometric_sums[OF `norm (1 - x) < 1`] by (rule sums_unique)
```
```  1364     also have "\<dots> = suminf (?f' x)"
```
```  1365       unfolding power_mult_distrib[symmetric]
```
```  1366       by (rule arg_cong[where f=suminf], rule arg_cong[where f="op ^"], auto)
```
```  1367     finally have "DERIV ln x :> suminf (?f' x)"
```
```  1368       using DERIV_ln[OF `0 < x`] unfolding divide_inverse by auto
```
```  1369     moreover
```
```  1370     have repos: "\<And> h x :: real. h - 1 + x = h + x - 1" by auto
```
```  1371     have "DERIV (\<lambda>x. suminf (?f x)) (x - 1) :>
```
```  1372       (\<Sum>n. (-1)^n * (1 / real (n + 1)) * real (Suc n) * (x - 1) ^ n)"
```
```  1373     proof (rule DERIV_power_series')
```
```  1374       show "x - 1 \<in> {- 1<..<1}" and "(0 :: real) < 1"
```
```  1375         using `0 < x` `x < 2` by auto
```
```  1376       fix x :: real
```
```  1377       assume "x \<in> {- 1<..<1}"
```
```  1378       hence "norm (-x) < 1" by auto
```
```  1379       show "summable (\<lambda>n. -1 ^ n * (1 / real (n + 1)) * real (Suc n) * x ^ n)"
```
```  1380         unfolding One_nat_def
```
```  1381         by (auto simp add: power_mult_distrib[symmetric] summable_geometric[OF `norm (-x) < 1`])
```
```  1382     qed
```
```  1383     hence "DERIV (\<lambda>x. suminf (?f x)) (x - 1) :> suminf (?f' x)"
```
```  1384       unfolding One_nat_def by auto
```
```  1385     hence "DERIV (\<lambda>x. suminf (?f (x - 1))) x :> suminf (?f' x)"
```
```  1386       unfolding deriv_def repos .
```
```  1387     ultimately have "DERIV (\<lambda>x. ln x - suminf (?f (x - 1))) x :> (suminf (?f' x) - suminf (?f' x))"
```
```  1388       by (rule DERIV_diff)
```
```  1389     thus "DERIV (\<lambda>x. ln x - suminf (?f (x - 1))) x :> 0" by auto
```
```  1390   qed (auto simp add: assms)
```
```  1391   thus ?thesis by auto
```
```  1392 qed
```
```  1393
```
```  1394 lemma exp_first_two_terms: "exp x = 1 + x + (\<Sum> n. inverse(fact (n+2)) * (x ^ (n+2)))"
```
```  1395 proof -
```
```  1396   have "exp x = suminf (\<lambda>n. inverse(fact n) * (x ^ n))"
```
```  1397     by (simp add: exp_def)
```
```  1398   also from summable_exp have "... = (\<Sum> n::nat = 0 ..< 2. inverse(fact n) * (x ^ n)) +
```
```  1399       (\<Sum> n. inverse(fact(n+2)) * (x ^ (n+2)))" (is "_ = ?a + _")
```
```  1400     by (rule suminf_split_initial_segment)
```
```  1401   also have "?a = 1 + x"
```
```  1402     by (simp add: numeral_2_eq_2)
```
```  1403   finally show ?thesis .
```
```  1404 qed
```
```  1405
```
```  1406 lemma exp_bound: "0 <= (x::real) \<Longrightarrow> x <= 1 \<Longrightarrow> exp x <= 1 + x + x\<^sup>2"
```
```  1407 proof -
```
```  1408   assume a: "0 <= x"
```
```  1409   assume b: "x <= 1"
```
```  1410   {
```
```  1411     fix n :: nat
```
```  1412     have "2 * 2 ^ n \<le> fact (n + 2)"
```
```  1413       by (induct n) simp_all
```
```  1414     hence "real ((2::nat) * 2 ^ n) \<le> real (fact (n + 2))"
```
```  1415       by (simp only: real_of_nat_le_iff)
```
```  1416     hence "2 * 2 ^ n \<le> real (fact (n + 2))"
```
```  1417       by simp
```
```  1418     hence "inverse (fact (n + 2)) \<le> inverse (2 * 2 ^ n)"
```
```  1419       by (rule le_imp_inverse_le) simp
```
```  1420     hence "inverse (fact (n + 2)) \<le> 1/2 * (1/2)^n"
```
```  1421       by (simp add: power_inverse)
```
```  1422     hence "inverse (fact (n + 2)) * (x^n * x\<^sup>2) \<le> 1/2 * (1/2)^n * (1 * x\<^sup>2)"
```
```  1423       by (rule mult_mono)
```
```  1424         (rule mult_mono, simp_all add: power_le_one a b mult_nonneg_nonneg)
```
```  1425     hence "inverse (fact (n + 2)) * x ^ (n + 2) \<le> (x\<^sup>2/2) * ((1/2)^n)"
```
```  1426       unfolding power_add by (simp add: mult_ac del: fact_Suc) }
```
```  1427   note aux1 = this
```
```  1428   have "(\<lambda>n. x\<^sup>2 / 2 * (1 / 2) ^ n) sums (x\<^sup>2 / 2 * (1 / (1 - 1 / 2)))"
```
```  1429     by (intro sums_mult geometric_sums, simp)
```
```  1430   hence aux2: "(\<lambda>n. x\<^sup>2 / 2 * (1 / 2) ^ n) sums x\<^sup>2"
```
```  1431     by simp
```
```  1432   have "suminf (\<lambda>n. inverse(fact (n+2)) * (x ^ (n+2))) <= x\<^sup>2"
```
```  1433   proof -
```
```  1434     have "suminf (\<lambda>n. inverse(fact (n+2)) * (x ^ (n+2))) <=
```
```  1435         suminf (\<lambda>n. (x\<^sup>2/2) * ((1/2)^n))"
```
```  1436       apply (rule summable_le)
```
```  1437       apply (rule allI, rule aux1)
```
```  1438       apply (rule summable_exp [THEN summable_ignore_initial_segment])
```
```  1439       by (rule sums_summable, rule aux2)
```
```  1440     also have "... = x\<^sup>2"
```
```  1441       by (rule sums_unique [THEN sym], rule aux2)
```
```  1442     finally show ?thesis .
```
```  1443   qed
```
```  1444   thus ?thesis unfolding exp_first_two_terms by auto
```
```  1445 qed
```
```  1446
```
```  1447 lemma ln_one_minus_pos_upper_bound: "0 <= x \<Longrightarrow> x < 1 \<Longrightarrow> ln (1 - x) <= - x"
```
```  1448 proof -
```
```  1449   assume a: "0 <= (x::real)" and b: "x < 1"
```
```  1450   have "(1 - x) * (1 + x + x\<^sup>2) = (1 - x^3)"
```
```  1451     by (simp add: algebra_simps power2_eq_square power3_eq_cube)
```
```  1452   also have "... <= 1"
```
```  1453     by (auto simp add: a)
```
```  1454   finally have "(1 - x) * (1 + x + x\<^sup>2) <= 1" .
```
```  1455   moreover have c: "0 < 1 + x + x\<^sup>2"
```
```  1456     by (simp add: add_pos_nonneg a)
```
```  1457   ultimately have "1 - x <= 1 / (1 + x + x\<^sup>2)"
```
```  1458     by (elim mult_imp_le_div_pos)
```
```  1459   also have "... <= 1 / exp x"
```
```  1460     by (metis a abs_one b exp_bound exp_gt_zero frac_le less_eq_real_def real_sqrt_abs
```
```  1461               real_sqrt_pow2_iff real_sqrt_power)
```
```  1462   also have "... = exp (-x)"
```
```  1463     by (auto simp add: exp_minus divide_inverse)
```
```  1464   finally have "1 - x <= exp (- x)" .
```
```  1465   also have "1 - x = exp (ln (1 - x))"
```
```  1466     by (metis b diff_0 exp_ln_iff less_iff_diff_less_0 minus_diff_eq)
```
```  1467   finally have "exp (ln (1 - x)) <= exp (- x)" .
```
```  1468   thus ?thesis by (auto simp only: exp_le_cancel_iff)
```
```  1469 qed
```
```  1470
```
```  1471 lemma exp_ge_add_one_self [simp]: "1 + (x::real) <= exp x"
```
```  1472   apply (case_tac "0 <= x")
```
```  1473   apply (erule exp_ge_add_one_self_aux)
```
```  1474   apply (case_tac "x <= -1")
```
```  1475   apply (subgoal_tac "1 + x <= 0")
```
```  1476   apply (erule order_trans)
```
```  1477   apply simp
```
```  1478   apply simp
```
```  1479   apply (subgoal_tac "1 + x = exp(ln (1 + x))")
```
```  1480   apply (erule ssubst)
```
```  1481   apply (subst exp_le_cancel_iff)
```
```  1482   apply (subgoal_tac "ln (1 - (- x)) <= - (- x)")
```
```  1483   apply simp
```
```  1484   apply (rule ln_one_minus_pos_upper_bound)
```
```  1485   apply auto
```
```  1486 done
```
```  1487
```
```  1488 lemma ln_one_plus_pos_lower_bound: "0 <= x \<Longrightarrow> x <= 1 \<Longrightarrow> x - x\<^sup>2 <= ln (1 + x)"
```
```  1489 proof -
```
```  1490   assume a: "0 <= x" and b: "x <= 1"
```
```  1491   have "exp (x - x\<^sup>2) = exp x / exp (x\<^sup>2)"
```
```  1492     by (rule exp_diff)
```
```  1493   also have "... <= (1 + x + x\<^sup>2) / exp (x \<^sup>2)"
```
```  1494     by (metis a b divide_right_mono exp_bound exp_ge_zero)
```
```  1495   also have "... <= (1 + x + x\<^sup>2) / (1 + x\<^sup>2)"
```
```  1496     by (simp add: a divide_left_mono mult_pos_pos add_pos_nonneg)
```
```  1497   also from a have "... <= 1 + x"
```
```  1498     by (simp add: field_simps add_strict_increasing zero_le_mult_iff)
```
```  1499   finally have "exp (x - x\<^sup>2) <= 1 + x" .
```
```  1500   also have "... = exp (ln (1 + x))"
```
```  1501   proof -
```
```  1502     from a have "0 < 1 + x" by auto
```
```  1503     thus ?thesis
```
```  1504       by (auto simp only: exp_ln_iff [THEN sym])
```
```  1505   qed
```
```  1506   finally have "exp (x - x\<^sup>2) <= exp (ln (1 + x))" .
```
```  1507   thus ?thesis
```
```  1508     by (metis exp_le_cancel_iff)
```
```  1509 qed
```
```  1510
```
```  1511 lemma ln_one_minus_pos_lower_bound:
```
```  1512   "0 <= x \<Longrightarrow> x <= (1 / 2) \<Longrightarrow> - x - 2 * x\<^sup>2 <= ln (1 - x)"
```
```  1513 proof -
```
```  1514   assume a: "0 <= x" and b: "x <= (1 / 2)"
```
```  1515   from b have c: "x < 1" by auto
```
```  1516   then have "ln (1 - x) = - ln (1 + x / (1 - x))"
```
```  1517     apply (subst ln_inverse [symmetric])
```
```  1518     apply (simp add: field_simps)
```
```  1519     apply (rule arg_cong [where f=ln])
```
```  1520     apply (simp add: field_simps)
```
```  1521     done
```
```  1522   also have "- (x / (1 - x)) <= ..."
```
```  1523   proof -
```
```  1524     have "ln (1 + x / (1 - x)) <= x / (1 - x)"
```
```  1525       apply (rule ln_add_one_self_le_self)
```
```  1526       apply (rule divide_nonneg_pos)
```
```  1527       using a c apply auto
```
```  1528       done
```
```  1529     thus ?thesis
```
```  1530       by auto
```
```  1531   qed
```
```  1532   also have "- (x / (1 - x)) = -x / (1 - x)"
```
```  1533     by auto
```
```  1534   finally have d: "- x / (1 - x) <= ln (1 - x)" .
```
```  1535   have "0 < 1 - x" using a b by simp
```
```  1536   hence e: "-x - 2 * x\<^sup>2 <= - x / (1 - x)"
```
```  1537     using mult_right_le_one_le[of "x*x" "2*x"] a b
```
```  1538     by (simp add: field_simps power2_eq_square)
```
```  1539   from e d show "- x - 2 * x\<^sup>2 <= ln (1 - x)"
```
```  1540     by (rule order_trans)
```
```  1541 qed
```
```  1542
```
```  1543 lemma ln_add_one_self_le_self2: "-1 < x \<Longrightarrow> ln(1 + x) <= x"
```
```  1544   apply (subgoal_tac "ln (1 + x) \<le> ln (exp x)", simp)
```
```  1545   apply (subst ln_le_cancel_iff)
```
```  1546   apply auto
```
```  1547   done
```
```  1548
```
```  1549 lemma abs_ln_one_plus_x_minus_x_bound_nonneg:
```
```  1550   "0 <= x \<Longrightarrow> x <= 1 \<Longrightarrow> abs(ln (1 + x) - x) <= x\<^sup>2"
```
```  1551 proof -
```
```  1552   assume x: "0 <= x"
```
```  1553   assume x1: "x <= 1"
```
```  1554   from x have "ln (1 + x) <= x"
```
```  1555     by (rule ln_add_one_self_le_self)
```
```  1556   then have "ln (1 + x) - x <= 0"
```
```  1557     by simp
```
```  1558   then have "abs(ln(1 + x) - x) = - (ln(1 + x) - x)"
```
```  1559     by (rule abs_of_nonpos)
```
```  1560   also have "... = x - ln (1 + x)"
```
```  1561     by simp
```
```  1562   also have "... <= x\<^sup>2"
```
```  1563   proof -
```
```  1564     from x x1 have "x - x\<^sup>2 <= ln (1 + x)"
```
```  1565       by (intro ln_one_plus_pos_lower_bound)
```
```  1566     thus ?thesis
```
```  1567       by simp
```
```  1568   qed
```
```  1569   finally show ?thesis .
```
```  1570 qed
```
```  1571
```
```  1572 lemma abs_ln_one_plus_x_minus_x_bound_nonpos:
```
```  1573   "-(1 / 2) <= x \<Longrightarrow> x <= 0 \<Longrightarrow> abs(ln (1 + x) - x) <= 2 * x\<^sup>2"
```
```  1574 proof -
```
```  1575   assume a: "-(1 / 2) <= x"
```
```  1576   assume b: "x <= 0"
```
```  1577   have "abs(ln (1 + x) - x) = x - ln(1 - (-x))"
```
```  1578     apply (subst abs_of_nonpos)
```
```  1579     apply simp
```
```  1580     apply (rule ln_add_one_self_le_self2)
```
```  1581     using a apply auto
```
```  1582     done
```
```  1583   also have "... <= 2 * x\<^sup>2"
```
```  1584     apply (subgoal_tac "- (-x) - 2 * (-x)\<^sup>2 <= ln (1 - (-x))")
```
```  1585     apply (simp add: algebra_simps)
```
```  1586     apply (rule ln_one_minus_pos_lower_bound)
```
```  1587     using a b apply auto
```
```  1588     done
```
```  1589   finally show ?thesis .
```
```  1590 qed
```
```  1591
```
```  1592 lemma abs_ln_one_plus_x_minus_x_bound:
```
```  1593     "abs x <= 1 / 2 \<Longrightarrow> abs(ln (1 + x) - x) <= 2 * x\<^sup>2"
```
```  1594   apply (case_tac "0 <= x")
```
```  1595   apply (rule order_trans)
```
```  1596   apply (rule abs_ln_one_plus_x_minus_x_bound_nonneg)
```
```  1597   apply auto
```
```  1598   apply (rule abs_ln_one_plus_x_minus_x_bound_nonpos)
```
```  1599   apply auto
```
```  1600   done
```
```  1601
```
```  1602 lemma ln_x_over_x_mono: "exp 1 <= x \<Longrightarrow> x <= y \<Longrightarrow> (ln y / y) <= (ln x / x)"
```
```  1603 proof -
```
```  1604   assume x: "exp 1 <= x" "x <= y"
```
```  1605   moreover have "0 < exp (1::real)" by simp
```
```  1606   ultimately have a: "0 < x" and b: "0 < y"
```
```  1607     by (fast intro: less_le_trans order_trans)+
```
```  1608   have "x * ln y - x * ln x = x * (ln y - ln x)"
```
```  1609     by (simp add: algebra_simps)
```
```  1610   also have "... = x * ln(y / x)"
```
```  1611     by (simp only: ln_div a b)
```
```  1612   also have "y / x = (x + (y - x)) / x"
```
```  1613     by simp
```
```  1614   also have "... = 1 + (y - x) / x"
```
```  1615     using x a by (simp add: field_simps)
```
```  1616   also have "x * ln(1 + (y - x) / x) <= x * ((y - x) / x)"
```
```  1617     apply (rule mult_left_mono)
```
```  1618     apply (rule ln_add_one_self_le_self)
```
```  1619     apply (rule divide_nonneg_pos)
```
```  1620     using x a apply simp_all
```
```  1621     done
```
```  1622   also have "... = y - x" using a by simp
```
```  1623   also have "... = (y - x) * ln (exp 1)" by simp
```
```  1624   also have "... <= (y - x) * ln x"
```
```  1625     apply (rule mult_left_mono)
```
```  1626     apply (subst ln_le_cancel_iff)
```
```  1627     apply fact
```
```  1628     apply (rule a)
```
```  1629     apply (rule x)
```
```  1630     using x apply simp
```
```  1631     done
```
```  1632   also have "... = y * ln x - x * ln x"
```
```  1633     by (rule left_diff_distrib)
```
```  1634   finally have "x * ln y <= y * ln x"
```
```  1635     by arith
```
```  1636   then have "ln y <= (y * ln x) / x" using a by (simp add: field_simps)
```
```  1637   also have "... = y * (ln x / x)" by simp
```
```  1638   finally show ?thesis using b by (simp add: field_simps)
```
```  1639 qed
```
```  1640
```
```  1641 lemma ln_le_minus_one: "0 < x \<Longrightarrow> ln x \<le> x - 1"
```
```  1642   using exp_ge_add_one_self[of "ln x"] by simp
```
```  1643
```
```  1644 lemma ln_eq_minus_one:
```
```  1645   assumes "0 < x" "ln x = x - 1"
```
```  1646   shows "x = 1"
```
```  1647 proof -
```
```  1648   let ?l = "\<lambda>y. ln y - y + 1"
```
```  1649   have D: "\<And>x. 0 < x \<Longrightarrow> DERIV ?l x :> (1 / x - 1)"
```
```  1650     by (auto intro!: DERIV_intros)
```
```  1651
```
```  1652   show ?thesis
```
```  1653   proof (cases rule: linorder_cases)
```
```  1654     assume "x < 1"
```
```  1655     from dense[OF `x < 1`] obtain a where "x < a" "a < 1" by blast
```
```  1656     from `x < a` have "?l x < ?l a"
```
```  1657     proof (rule DERIV_pos_imp_increasing, safe)
```
```  1658       fix y
```
```  1659       assume "x \<le> y" "y \<le> a"
```
```  1660       with `0 < x` `a < 1` have "0 < 1 / y - 1" "0 < y"
```
```  1661         by (auto simp: field_simps)
```
```  1662       with D show "\<exists>z. DERIV ?l y :> z \<and> 0 < z"
```
```  1663         by auto
```
```  1664     qed
```
```  1665     also have "\<dots> \<le> 0"
```
```  1666       using ln_le_minus_one `0 < x` `x < a` by (auto simp: field_simps)
```
```  1667     finally show "x = 1" using assms by auto
```
```  1668   next
```
```  1669     assume "1 < x"
```
```  1670     from dense[OF this] obtain a where "1 < a" "a < x" by blast
```
```  1671     from `a < x` have "?l x < ?l a"
```
```  1672     proof (rule DERIV_neg_imp_decreasing, safe)
```
```  1673       fix y
```
```  1674       assume "a \<le> y" "y \<le> x"
```
```  1675       with `1 < a` have "1 / y - 1 < 0" "0 < y"
```
```  1676         by (auto simp: field_simps)
```
```  1677       with D show "\<exists>z. DERIV ?l y :> z \<and> z < 0"
```
```  1678         by blast
```
```  1679     qed
```
```  1680     also have "\<dots> \<le> 0"
```
```  1681       using ln_le_minus_one `1 < a` by (auto simp: field_simps)
```
```  1682     finally show "x = 1" using assms by auto
```
```  1683   next
```
```  1684     assume "x = 1"
```
```  1685     then show ?thesis by simp
```
```  1686   qed
```
```  1687 qed
```
```  1688
```
```  1689 lemma exp_at_bot: "(exp ---> (0::real)) at_bot"
```
```  1690   unfolding tendsto_Zfun_iff
```
```  1691 proof (rule ZfunI, simp add: eventually_at_bot_dense)
```
```  1692   fix r :: real assume "0 < r"
```
```  1693   {
```
```  1694     fix x
```
```  1695     assume "x < ln r"
```
```  1696     then have "exp x < exp (ln r)"
```
```  1697       by simp
```
```  1698     with `0 < r` have "exp x < r"
```
```  1699       by simp
```
```  1700   }
```
```  1701   then show "\<exists>k. \<forall>n<k. exp n < r" by auto
```
```  1702 qed
```
```  1703
```
```  1704 lemma exp_at_top: "LIM x at_top. exp x :: real :> at_top"
```
```  1705   by (rule filterlim_at_top_at_top[where Q="\<lambda>x. True" and P="\<lambda>x. 0 < x" and g="ln"])
```
```  1706      (auto intro: eventually_gt_at_top)
```
```  1707
```
```  1708 lemma ln_at_0: "LIM x at_right 0. ln x :> at_bot"
```
```  1709   by (rule filterlim_at_bot_at_right[where Q="\<lambda>x. 0 < x" and P="\<lambda>x. True" and g="exp"])
```
```  1710      (auto simp: eventually_at_filter)
```
```  1711
```
```  1712 lemma ln_at_top: "LIM x at_top. ln x :> at_top"
```
```  1713   by (rule filterlim_at_top_at_top[where Q="\<lambda>x. 0 < x" and P="\<lambda>x. True" and g="exp"])
```
```  1714      (auto intro: eventually_gt_at_top)
```
```  1715
```
```  1716 lemma tendsto_power_div_exp_0: "((\<lambda>x. x ^ k / exp x) ---> (0::real)) at_top"
```
```  1717 proof (induct k)
```
```  1718   case 0
```
```  1719   show "((\<lambda>x. x ^ 0 / exp x) ---> (0::real)) at_top"
```
```  1720     by (simp add: inverse_eq_divide[symmetric])
```
```  1721        (metis filterlim_compose[OF tendsto_inverse_0] exp_at_top filterlim_mono
```
```  1722               at_top_le_at_infinity order_refl)
```
```  1723 next
```
```  1724   case (Suc k)
```
```  1725   show ?case
```
```  1726   proof (rule lhospital_at_top_at_top)
```
```  1727     show "eventually (\<lambda>x. DERIV (\<lambda>x. x ^ Suc k) x :> (real (Suc k) * x^k)) at_top"
```
```  1728       by eventually_elim (intro DERIV_intros, simp, simp)
```
```  1729     show "eventually (\<lambda>x. DERIV exp x :> exp x) at_top"
```
```  1730       by eventually_elim (auto intro!: DERIV_intros)
```
```  1731     show "eventually (\<lambda>x. exp x \<noteq> 0) at_top"
```
```  1732       by auto
```
```  1733     from tendsto_mult[OF tendsto_const Suc, of "real (Suc k)"]
```
```  1734     show "((\<lambda>x. real (Suc k) * x ^ k / exp x) ---> 0) at_top"
```
```  1735       by simp
```
```  1736   qed (rule exp_at_top)
```
```  1737 qed
```
```  1738
```
```  1739
```
```  1740 definition powr :: "[real,real] => real"  (infixr "powr" 80)
```
```  1741   -- {*exponentation with real exponent*}
```
```  1742   where "x powr a = exp(a * ln x)"
```
```  1743
```
```  1744 definition log :: "[real,real] => real"
```
```  1745   -- {*logarithm of @{term x} to base @{term a}*}
```
```  1746   where "log a x = ln x / ln a"
```
```  1747
```
```  1748
```
```  1749 lemma tendsto_log [tendsto_intros]:
```
```  1750   "\<lbrakk>(f ---> a) F; (g ---> b) F; 0 < a; a \<noteq> 1; 0 < b\<rbrakk> \<Longrightarrow> ((\<lambda>x. log (f x) (g x)) ---> log a b) F"
```
```  1751   unfolding log_def by (intro tendsto_intros) auto
```
```  1752
```
```  1753 lemma continuous_log:
```
```  1754   assumes "continuous F f"
```
```  1755     and "continuous F g"
```
```  1756     and "0 < f (Lim F (\<lambda>x. x))"
```
```  1757     and "f (Lim F (\<lambda>x. x)) \<noteq> 1"
```
```  1758     and "0 < g (Lim F (\<lambda>x. x))"
```
```  1759   shows "continuous F (\<lambda>x. log (f x) (g x))"
```
```  1760   using assms unfolding continuous_def by (rule tendsto_log)
```
```  1761
```
```  1762 lemma continuous_at_within_log[continuous_intros]:
```
```  1763   assumes "continuous (at a within s) f"
```
```  1764     and "continuous (at a within s) g"
```
```  1765     and "0 < f a"
```
```  1766     and "f a \<noteq> 1"
```
```  1767     and "0 < g a"
```
```  1768   shows "continuous (at a within s) (\<lambda>x. log (f x) (g x))"
```
```  1769   using assms unfolding continuous_within by (rule tendsto_log)
```
```  1770
```
```  1771 lemma isCont_log[continuous_intros, simp]:
```
```  1772   assumes "isCont f a" "isCont g a" "0 < f a" "f a \<noteq> 1" "0 < g a"
```
```  1773   shows "isCont (\<lambda>x. log (f x) (g x)) a"
```
```  1774   using assms unfolding continuous_at by (rule tendsto_log)
```
```  1775
```
```  1776 lemma continuous_on_log[continuous_on_intros]:
```
```  1777   assumes "continuous_on s f" "continuous_on s g"
```
```  1778     and "\<forall>x\<in>s. 0 < f x" "\<forall>x\<in>s. f x \<noteq> 1" "\<forall>x\<in>s. 0 < g x"
```
```  1779   shows "continuous_on s (\<lambda>x. log (f x) (g x))"
```
```  1780   using assms unfolding continuous_on_def by (fast intro: tendsto_log)
```
```  1781
```
```  1782 lemma powr_one_eq_one [simp]: "1 powr a = 1"
```
```  1783   by (simp add: powr_def)
```
```  1784
```
```  1785 lemma powr_zero_eq_one [simp]: "x powr 0 = 1"
```
```  1786   by (simp add: powr_def)
```
```  1787
```
```  1788 lemma powr_one_gt_zero_iff [simp]: "(x powr 1 = x) = (0 < x)"
```
```  1789   by (simp add: powr_def)
```
```  1790 declare powr_one_gt_zero_iff [THEN iffD2, simp]
```
```  1791
```
```  1792 lemma powr_mult: "0 < x \<Longrightarrow> 0 < y \<Longrightarrow> (x * y) powr a = (x powr a) * (y powr a)"
```
```  1793   by (simp add: powr_def exp_add [symmetric] ln_mult distrib_left)
```
```  1794
```
```  1795 lemma powr_gt_zero [simp]: "0 < x powr a"
```
```  1796   by (simp add: powr_def)
```
```  1797
```
```  1798 lemma powr_ge_pzero [simp]: "0 <= x powr y"
```
```  1799   by (rule order_less_imp_le, rule powr_gt_zero)
```
```  1800
```
```  1801 lemma powr_not_zero [simp]: "x powr a \<noteq> 0"
```
```  1802   by (simp add: powr_def)
```
```  1803
```
```  1804 lemma powr_divide: "0 < x \<Longrightarrow> 0 < y \<Longrightarrow> (x / y) powr a = (x powr a) / (y powr a)"
```
```  1805   apply (simp add: divide_inverse positive_imp_inverse_positive powr_mult)
```
```  1806   apply (simp add: powr_def exp_minus [symmetric] exp_add [symmetric] ln_inverse)
```
```  1807   done
```
```  1808
```
```  1809 lemma powr_divide2: "x powr a / x powr b = x powr (a - b)"
```
```  1810   apply (simp add: powr_def)
```
```  1811   apply (subst exp_diff [THEN sym])
```
```  1812   apply (simp add: left_diff_distrib)
```
```  1813   done
```
```  1814
```
```  1815 lemma powr_add: "x powr (a + b) = (x powr a) * (x powr b)"
```
```  1816   by (simp add: powr_def exp_add [symmetric] distrib_right)
```
```  1817
```
```  1818 lemma powr_mult_base: "0 < x \<Longrightarrow>x * x powr y = x powr (1 + y)"
```
```  1819   using assms by (auto simp: powr_add)
```
```  1820
```
```  1821 lemma powr_powr: "(x powr a) powr b = x powr (a * b)"
```
```  1822   by (simp add: powr_def)
```
```  1823
```
```  1824 lemma powr_powr_swap: "(x powr a) powr b = (x powr b) powr a"
```
```  1825   by (simp add: powr_powr mult_commute)
```
```  1826
```
```  1827 lemma powr_minus: "x powr (-a) = inverse (x powr a)"
```
```  1828   by (simp add: powr_def exp_minus [symmetric])
```
```  1829
```
```  1830 lemma powr_minus_divide: "x powr (-a) = 1/(x powr a)"
```
```  1831   by (simp add: divide_inverse powr_minus)
```
```  1832
```
```  1833 lemma powr_less_mono: "a < b \<Longrightarrow> 1 < x \<Longrightarrow> x powr a < x powr b"
```
```  1834   by (simp add: powr_def)
```
```  1835
```
```  1836 lemma powr_less_cancel: "x powr a < x powr b \<Longrightarrow> 1 < x \<Longrightarrow> a < b"
```
```  1837   by (simp add: powr_def)
```
```  1838
```
```  1839 lemma powr_less_cancel_iff [simp]: "1 < x \<Longrightarrow> (x powr a < x powr b) = (a < b)"
```
```  1840   by (blast intro: powr_less_cancel powr_less_mono)
```
```  1841
```
```  1842 lemma powr_le_cancel_iff [simp]: "1 < x \<Longrightarrow> (x powr a \<le> x powr b) = (a \<le> b)"
```
```  1843   by (simp add: linorder_not_less [symmetric])
```
```  1844
```
```  1845 lemma log_ln: "ln x = log (exp(1)) x"
```
```  1846   by (simp add: log_def)
```
```  1847
```
```  1848 lemma DERIV_log:
```
```  1849   assumes "x > 0"
```
```  1850   shows "DERIV (\<lambda>y. log b y) x :> 1 / (ln b * x)"
```
```  1851 proof -
```
```  1852   def lb \<equiv> "1 / ln b"
```
```  1853   moreover have "DERIV (\<lambda>y. lb * ln y) x :> lb / x"
```
```  1854     using `x > 0` by (auto intro!: DERIV_intros)
```
```  1855   ultimately show ?thesis
```
```  1856     by (simp add: log_def)
```
```  1857 qed
```
```  1858
```
```  1859 lemmas DERIV_log[THEN DERIV_chain2, THEN DERIV_cong, DERIV_intros]
```
```  1860
```
```  1861 lemma powr_log_cancel [simp]: "0 < a \<Longrightarrow> a \<noteq> 1 \<Longrightarrow> 0 < x \<Longrightarrow> a powr (log a x) = x"
```
```  1862   by (simp add: powr_def log_def)
```
```  1863
```
```  1864 lemma log_powr_cancel [simp]: "0 < a \<Longrightarrow> a \<noteq> 1 \<Longrightarrow> log a (a powr y) = y"
```
```  1865   by (simp add: log_def powr_def)
```
```  1866
```
```  1867 lemma log_mult:
```
```  1868   "0 < a \<Longrightarrow> a \<noteq> 1 \<Longrightarrow> 0 < x \<Longrightarrow> 0 < y \<Longrightarrow>
```
```  1869     log a (x * y) = log a x + log a y"
```
```  1870   by (simp add: log_def ln_mult divide_inverse distrib_right)
```
```  1871
```
```  1872 lemma log_eq_div_ln_mult_log:
```
```  1873   "0 < a \<Longrightarrow> a \<noteq> 1 \<Longrightarrow> 0 < b \<Longrightarrow> b \<noteq> 1 \<Longrightarrow> 0 < x \<Longrightarrow>
```
```  1874     log a x = (ln b/ln a) * log b x"
```
```  1875   by (simp add: log_def divide_inverse)
```
```  1876
```
```  1877 text{*Base 10 logarithms*}
```
```  1878 lemma log_base_10_eq1: "0 < x \<Longrightarrow> log 10 x = (ln (exp 1) / ln 10) * ln x"
```
```  1879   by (simp add: log_def)
```
```  1880
```
```  1881 lemma log_base_10_eq2: "0 < x \<Longrightarrow> log 10 x = (log 10 (exp 1)) * ln x"
```
```  1882   by (simp add: log_def)
```
```  1883
```
```  1884 lemma log_one [simp]: "log a 1 = 0"
```
```  1885   by (simp add: log_def)
```
```  1886
```
```  1887 lemma log_eq_one [simp]: "[| 0 < a; a \<noteq> 1 |] ==> log a a = 1"
```
```  1888   by (simp add: log_def)
```
```  1889
```
```  1890 lemma log_inverse: "0 < a \<Longrightarrow> a \<noteq> 1 \<Longrightarrow> 0 < x \<Longrightarrow> log a (inverse x) = - log a x"
```
```  1891   apply (rule_tac a1 = "log a x" in add_left_cancel [THEN iffD1])
```
```  1892   apply (simp add: log_mult [symmetric])
```
```  1893   done
```
```  1894
```
```  1895 lemma log_divide: "0 < a \<Longrightarrow> a \<noteq> 1 \<Longrightarrow> 0 < x \<Longrightarrow> 0 < y \<Longrightarrow> log a (x/y) = log a x - log a y"
```
```  1896   by (simp add: log_mult divide_inverse log_inverse)
```
```  1897
```
```  1898 lemma log_less_cancel_iff [simp]:
```
```  1899   "1 < a \<Longrightarrow> 0 < x \<Longrightarrow> 0 < y \<Longrightarrow> log a x < log a y \<longleftrightarrow> x < y"
```
```  1900   apply safe
```
```  1901   apply (rule_tac [2] powr_less_cancel)
```
```  1902   apply (drule_tac a = "log a x" in powr_less_mono, auto)
```
```  1903   done
```
```  1904
```
```  1905 lemma log_inj:
```
```  1906   assumes "1 < b"
```
```  1907   shows "inj_on (log b) {0 <..}"
```
```  1908 proof (rule inj_onI, simp)
```
```  1909   fix x y
```
```  1910   assume pos: "0 < x" "0 < y" and *: "log b x = log b y"
```
```  1911   show "x = y"
```
```  1912   proof (cases rule: linorder_cases)
```
```  1913     assume "x = y"
```
```  1914     then show ?thesis by simp
```
```  1915   next
```
```  1916     assume "x < y" hence "log b x < log b y"
```
```  1917       using log_less_cancel_iff[OF `1 < b`] pos by simp
```
```  1918     then show ?thesis using * by simp
```
```  1919   next
```
```  1920     assume "y < x" hence "log b y < log b x"
```
```  1921       using log_less_cancel_iff[OF `1 < b`] pos by simp
```
```  1922     then show ?thesis using * by simp
```
```  1923   qed
```
```  1924 qed
```
```  1925
```
```  1926 lemma log_le_cancel_iff [simp]:
```
```  1927   "1 < a \<Longrightarrow> 0 < x \<Longrightarrow> 0 < y \<Longrightarrow> (log a x \<le> log a y) = (x \<le> y)"
```
```  1928   by (simp add: linorder_not_less [symmetric])
```
```  1929
```
```  1930 lemma zero_less_log_cancel_iff[simp]: "1 < a \<Longrightarrow> 0 < x \<Longrightarrow> 0 < log a x \<longleftrightarrow> 1 < x"
```
```  1931   using log_less_cancel_iff[of a 1 x] by simp
```
```  1932
```
```  1933 lemma zero_le_log_cancel_iff[simp]: "1 < a \<Longrightarrow> 0 < x \<Longrightarrow> 0 \<le> log a x \<longleftrightarrow> 1 \<le> x"
```
```  1934   using log_le_cancel_iff[of a 1 x] by simp
```
```  1935
```
```  1936 lemma log_less_zero_cancel_iff[simp]: "1 < a \<Longrightarrow> 0 < x \<Longrightarrow> log a x < 0 \<longleftrightarrow> x < 1"
```
```  1937   using log_less_cancel_iff[of a x 1] by simp
```
```  1938
```
```  1939 lemma log_le_zero_cancel_iff[simp]: "1 < a \<Longrightarrow> 0 < x \<Longrightarrow> log a x \<le> 0 \<longleftrightarrow> x \<le> 1"
```
```  1940   using log_le_cancel_iff[of a x 1] by simp
```
```  1941
```
```  1942 lemma one_less_log_cancel_iff[simp]: "1 < a \<Longrightarrow> 0 < x \<Longrightarrow> 1 < log a x \<longleftrightarrow> a < x"
```
```  1943   using log_less_cancel_iff[of a a x] by simp
```
```  1944
```
```  1945 lemma one_le_log_cancel_iff[simp]: "1 < a \<Longrightarrow> 0 < x \<Longrightarrow> 1 \<le> log a x \<longleftrightarrow> a \<le> x"
```
```  1946   using log_le_cancel_iff[of a a x] by simp
```
```  1947
```
```  1948 lemma log_less_one_cancel_iff[simp]: "1 < a \<Longrightarrow> 0 < x \<Longrightarrow> log a x < 1 \<longleftrightarrow> x < a"
```
```  1949   using log_less_cancel_iff[of a x a] by simp
```
```  1950
```
```  1951 lemma log_le_one_cancel_iff[simp]: "1 < a \<Longrightarrow> 0 < x \<Longrightarrow> log a x \<le> 1 \<longleftrightarrow> x \<le> a"
```
```  1952   using log_le_cancel_iff[of a x a] by simp
```
```  1953
```
```  1954 lemma powr_realpow: "0 < x ==> x powr (real n) = x^n"
```
```  1955   apply (induct n)
```
```  1956   apply simp
```
```  1957   apply (subgoal_tac "real(Suc n) = real n + 1")
```
```  1958   apply (erule ssubst)
```
```  1959   apply (subst powr_add, simp, simp)
```
```  1960   done
```
```  1961
```
```  1962 lemma powr_realpow_numeral: "0 < x \<Longrightarrow> x powr (numeral n :: real) = x ^ (numeral n)"
```
```  1963   unfolding real_of_nat_numeral [symmetric] by (rule powr_realpow)
```
```  1964
```
```  1965 lemma powr_realpow2: "0 <= x ==> 0 < n ==> x^n = (if (x = 0) then 0 else x powr (real n))"
```
```  1966   apply (case_tac "x = 0", simp, simp)
```
```  1967   apply (rule powr_realpow [THEN sym], simp)
```
```  1968   done
```
```  1969
```
```  1970 lemma powr_int:
```
```  1971   assumes "x > 0"
```
```  1972   shows "x powr i = (if i \<ge> 0 then x ^ nat i else 1 / x ^ nat (-i))"
```
```  1973 proof (cases "i < 0")
```
```  1974   case True
```
```  1975   have r: "x powr i = 1 / x powr (-i)" by (simp add: powr_minus field_simps)
```
```  1976   show ?thesis using `i < 0` `x > 0` by (simp add: r field_simps powr_realpow[symmetric])
```
```  1977 next
```
```  1978   case False
```
```  1979   then show ?thesis by (simp add: assms powr_realpow[symmetric])
```
```  1980 qed
```
```  1981
```
```  1982 lemma powr_one: "0 < x \<Longrightarrow> x powr 1 = x"
```
```  1983   using powr_realpow [of x 1] by simp
```
```  1984
```
```  1985 lemma powr_numeral: "0 < x \<Longrightarrow> x powr numeral n = x ^ numeral n"
```
```  1986   by (fact powr_realpow_numeral)
```
```  1987
```
```  1988 lemma powr_neg_one: "0 < x \<Longrightarrow> x powr - 1 = 1 / x"
```
```  1989   using powr_int [of x "- 1"] by simp
```
```  1990
```
```  1991 lemma powr_neg_numeral: "0 < x \<Longrightarrow> x powr - numeral n = 1 / x ^ numeral n"
```
```  1992   using powr_int [of x "- numeral n"] by simp
```
```  1993
```
```  1994 lemma root_powr_inverse: "0 < n \<Longrightarrow> 0 < x \<Longrightarrow> root n x = x powr (1/n)"
```
```  1995   by (rule real_root_pos_unique) (auto simp: powr_realpow[symmetric] powr_powr)
```
```  1996
```
```  1997 lemma ln_powr: "0 < x ==> 0 < y ==> ln(x powr y) = y * ln x"
```
```  1998   unfolding powr_def by simp
```
```  1999
```
```  2000 lemma log_powr: "0 < x ==> 0 \<le> y ==> log b (x powr y) = y * log b x"
```
```  2001   apply (cases "y = 0")
```
```  2002   apply force
```
```  2003   apply (auto simp add: log_def ln_powr field_simps)
```
```  2004   done
```
```  2005
```
```  2006 lemma log_nat_power: "0 < x ==> log b (x^n) = real n * log b x"
```
```  2007   apply (subst powr_realpow [symmetric])
```
```  2008   apply (auto simp add: log_powr)
```
```  2009   done
```
```  2010
```
```  2011 lemma ln_bound: "1 <= x ==> ln x <= x"
```
```  2012   apply (subgoal_tac "ln(1 + (x - 1)) <= x - 1")
```
```  2013   apply simp
```
```  2014   apply (rule ln_add_one_self_le_self, simp)
```
```  2015   done
```
```  2016
```
```  2017 lemma powr_mono: "a <= b ==> 1 <= x ==> x powr a <= x powr b"
```
```  2018   apply (cases "x = 1", simp)
```
```  2019   apply (cases "a = b", simp)
```
```  2020   apply (rule order_less_imp_le)
```
```  2021   apply (rule powr_less_mono, auto)
```
```  2022   done
```
```  2023
```
```  2024 lemma ge_one_powr_ge_zero: "1 <= x ==> 0 <= a ==> 1 <= x powr a"
```
```  2025   apply (subst powr_zero_eq_one [THEN sym])
```
```  2026   apply (rule powr_mono, assumption+)
```
```  2027   done
```
```  2028
```
```  2029 lemma powr_less_mono2: "0 < a ==> 0 < x ==> x < y ==> x powr a < y powr a"
```
```  2030   apply (unfold powr_def)
```
```  2031   apply (rule exp_less_mono)
```
```  2032   apply (rule mult_strict_left_mono)
```
```  2033   apply (subst ln_less_cancel_iff, assumption)
```
```  2034   apply (rule order_less_trans)
```
```  2035   prefer 2
```
```  2036   apply assumption+
```
```  2037   done
```
```  2038
```
```  2039 lemma powr_less_mono2_neg: "a < 0 ==> 0 < x ==> x < y ==> y powr a < x powr a"
```
```  2040   apply (unfold powr_def)
```
```  2041   apply (rule exp_less_mono)
```
```  2042   apply (rule mult_strict_left_mono_neg)
```
```  2043   apply (subst ln_less_cancel_iff)
```
```  2044   apply assumption
```
```  2045   apply (rule order_less_trans)
```
```  2046   prefer 2
```
```  2047   apply assumption+
```
```  2048   done
```
```  2049
```
```  2050 lemma powr_mono2: "0 <= a ==> 0 < x ==> x <= y ==> x powr a <= y powr a"
```
```  2051   apply (case_tac "a = 0", simp)
```
```  2052   apply (case_tac "x = y", simp)
```
```  2053   apply (metis less_eq_real_def powr_less_mono2)
```
```  2054   done
```
```  2055
```
```  2056 lemma powr_inj: "0 < a \<Longrightarrow> a \<noteq> 1 \<Longrightarrow> a powr x = a powr y \<longleftrightarrow> x = y"
```
```  2057   unfolding powr_def exp_inj_iff by simp
```
```  2058
```
```  2059 lemma ln_powr_bound: "1 <= x ==> 0 < a ==> ln x <= (x powr a) / a"
```
```  2060   by (metis less_eq_real_def ln_less_self mult_imp_le_div_pos ln_powr mult_commute
```
```  2061             order.strict_trans2 powr_gt_zero zero_less_one)
```
```  2062
```
```  2063 lemma ln_powr_bound2:
```
```  2064   assumes "1 < x" and "0 < a"
```
```  2065   shows "(ln x) powr a <= (a powr a) * x"
```
```  2066 proof -
```
```  2067   from assms have "ln x <= (x powr (1 / a)) / (1 / a)"
```
```  2068     by (metis less_eq_real_def ln_powr_bound zero_less_divide_1_iff)
```
```  2069   also have "... = a * (x powr (1 / a))"
```
```  2070     by simp
```
```  2071   finally have "(ln x) powr a <= (a * (x powr (1 / a))) powr a"
```
```  2072     by (metis assms less_imp_le ln_gt_zero powr_mono2)
```
```  2073   also have "... = (a powr a) * ((x powr (1 / a)) powr a)"
```
```  2074     by (metis assms(2) powr_mult powr_gt_zero)
```
```  2075   also have "(x powr (1 / a)) powr a = x powr ((1 / a) * a)"
```
```  2076     by (rule powr_powr)
```
```  2077   also have "... = x" using assms
```
```  2078     by auto
```
```  2079   finally show ?thesis .
```
```  2080 qed
```
```  2081
```
```  2082 lemma tendsto_powr [tendsto_intros]:
```
```  2083   "\<lbrakk>(f ---> a) F; (g ---> b) F; 0 < a\<rbrakk> \<Longrightarrow> ((\<lambda>x. f x powr g x) ---> a powr b) F"
```
```  2084   unfolding powr_def by (intro tendsto_intros)
```
```  2085
```
```  2086 lemma continuous_powr:
```
```  2087   assumes "continuous F f"
```
```  2088     and "continuous F g"
```
```  2089     and "0 < f (Lim F (\<lambda>x. x))"
```
```  2090   shows "continuous F (\<lambda>x. (f x) powr (g x))"
```
```  2091   using assms unfolding continuous_def by (rule tendsto_powr)
```
```  2092
```
```  2093 lemma continuous_at_within_powr[continuous_intros]:
```
```  2094   assumes "continuous (at a within s) f"
```
```  2095     and "continuous (at a within s) g"
```
```  2096     and "0 < f a"
```
```  2097   shows "continuous (at a within s) (\<lambda>x. (f x) powr (g x))"
```
```  2098   using assms unfolding continuous_within by (rule tendsto_powr)
```
```  2099
```
```  2100 lemma isCont_powr[continuous_intros, simp]:
```
```  2101   assumes "isCont f a" "isCont g a" "0 < f a"
```
```  2102   shows "isCont (\<lambda>x. (f x) powr g x) a"
```
```  2103   using assms unfolding continuous_at by (rule tendsto_powr)
```
```  2104
```
```  2105 lemma continuous_on_powr[continuous_on_intros]:
```
```  2106   assumes "continuous_on s f" "continuous_on s g" and "\<forall>x\<in>s. 0 < f x"
```
```  2107   shows "continuous_on s (\<lambda>x. (f x) powr (g x))"
```
```  2108   using assms unfolding continuous_on_def by (fast intro: tendsto_powr)
```
```  2109
```
```  2110 (* FIXME: generalize by replacing d by with g x and g ---> d? *)
```
```  2111 lemma tendsto_zero_powrI:
```
```  2112   assumes "eventually (\<lambda>x. 0 < f x ) F" and "(f ---> 0) F"
```
```  2113     and "0 < d"
```
```  2114   shows "((\<lambda>x. f x powr d) ---> 0) F"
```
```  2115 proof (rule tendstoI)
```
```  2116   fix e :: real assume "0 < e"
```
```  2117   def Z \<equiv> "e powr (1 / d)"
```
```  2118   with `0 < e` have "0 < Z" by simp
```
```  2119   with assms have "eventually (\<lambda>x. 0 < f x \<and> dist (f x) 0 < Z) F"
```
```  2120     by (intro eventually_conj tendstoD)
```
```  2121   moreover
```
```  2122   from assms have "\<And>x. 0 < x \<and> dist x 0 < Z \<Longrightarrow> x powr d < Z powr d"
```
```  2123     by (intro powr_less_mono2) (auto simp: dist_real_def)
```
```  2124   with assms `0 < e` have "\<And>x. 0 < x \<and> dist x 0 < Z \<Longrightarrow> dist (x powr d) 0 < e"
```
```  2125     unfolding dist_real_def Z_def by (auto simp: powr_powr)
```
```  2126   ultimately
```
```  2127   show "eventually (\<lambda>x. dist (f x powr d) 0 < e) F" by (rule eventually_elim1)
```
```  2128 qed
```
```  2129
```
```  2130 lemma tendsto_neg_powr:
```
```  2131   assumes "s < 0"
```
```  2132     and "LIM x F. f x :> at_top"
```
```  2133   shows "((\<lambda>x. f x powr s) ---> 0) F"
```
```  2134 proof (rule tendstoI)
```
```  2135   fix e :: real assume "0 < e"
```
```  2136   def Z \<equiv> "e powr (1 / s)"
```
```  2137   from assms have "eventually (\<lambda>x. Z < f x) F"
```
```  2138     by (simp add: filterlim_at_top_dense)
```
```  2139   moreover
```
```  2140   from assms have "\<And>x. Z < x \<Longrightarrow> x powr s < Z powr s"
```
```  2141     by (auto simp: Z_def intro!: powr_less_mono2_neg)
```
```  2142   with assms `0 < e` have "\<And>x. Z < x \<Longrightarrow> dist (x powr s) 0 < e"
```
```  2143     by (simp add: powr_powr Z_def dist_real_def)
```
```  2144   ultimately
```
```  2145   show "eventually (\<lambda>x. dist (f x powr s) 0 < e) F" by (rule eventually_elim1)
```
```  2146 qed
```
```  2147
```
```  2148 subsection {* Sine and Cosine *}
```
```  2149
```
```  2150 definition sin_coeff :: "nat \<Rightarrow> real" where
```
```  2151   "sin_coeff = (\<lambda>n. if even n then 0 else -1 ^ ((n - Suc 0) div 2) / real (fact n))"
```
```  2152
```
```  2153 definition cos_coeff :: "nat \<Rightarrow> real" where
```
```  2154   "cos_coeff = (\<lambda>n. if even n then (-1 ^ (n div 2)) / real (fact n) else 0)"
```
```  2155
```
```  2156 definition sin :: "real \<Rightarrow> real"
```
```  2157   where "sin = (\<lambda>x. \<Sum>n. sin_coeff n * x ^ n)"
```
```  2158
```
```  2159 definition cos :: "real \<Rightarrow> real"
```
```  2160   where "cos = (\<lambda>x. \<Sum>n. cos_coeff n * x ^ n)"
```
```  2161
```
```  2162 lemma sin_coeff_0 [simp]: "sin_coeff 0 = 0"
```
```  2163   unfolding sin_coeff_def by simp
```
```  2164
```
```  2165 lemma cos_coeff_0 [simp]: "cos_coeff 0 = 1"
```
```  2166   unfolding cos_coeff_def by simp
```
```  2167
```
```  2168 lemma sin_coeff_Suc: "sin_coeff (Suc n) = cos_coeff n / real (Suc n)"
```
```  2169   unfolding cos_coeff_def sin_coeff_def
```
```  2170   by (simp del: mult_Suc)
```
```  2171
```
```  2172 lemma cos_coeff_Suc: "cos_coeff (Suc n) = - sin_coeff n / real (Suc n)"
```
```  2173   unfolding cos_coeff_def sin_coeff_def
```
```  2174   by (simp del: mult_Suc, auto simp add: odd_Suc_mult_two_ex)
```
```  2175
```
```  2176 lemma summable_sin: "summable (\<lambda>n. sin_coeff n * x ^ n)"
```
```  2177   unfolding sin_coeff_def
```
```  2178   apply (rule summable_comparison_test [OF _ summable_exp [where x="\<bar>x\<bar>"]])
```
```  2179   apply (auto simp add: divide_inverse abs_mult power_abs [symmetric] zero_le_mult_iff)
```
```  2180   done
```
```  2181
```
```  2182 lemma summable_cos: "summable (\<lambda>n. cos_coeff n * x ^ n)"
```
```  2183   unfolding cos_coeff_def
```
```  2184   apply (rule summable_comparison_test [OF _ summable_exp [where x="\<bar>x\<bar>"]])
```
```  2185   apply (auto simp add: divide_inverse abs_mult power_abs [symmetric] zero_le_mult_iff)
```
```  2186   done
```
```  2187
```
```  2188 lemma sin_converges: "(\<lambda>n. sin_coeff n * x ^ n) sums sin(x)"
```
```  2189   unfolding sin_def by (rule summable_sin [THEN summable_sums])
```
```  2190
```
```  2191 lemma cos_converges: "(\<lambda>n. cos_coeff n * x ^ n) sums cos(x)"
```
```  2192   unfolding cos_def by (rule summable_cos [THEN summable_sums])
```
```  2193
```
```  2194 lemma diffs_sin_coeff: "diffs sin_coeff = cos_coeff"
```
```  2195   by (simp add: diffs_def sin_coeff_Suc real_of_nat_def del: of_nat_Suc)
```
```  2196
```
```  2197 lemma diffs_cos_coeff: "diffs cos_coeff = (\<lambda>n. - sin_coeff n)"
```
```  2198   by (simp add: diffs_def cos_coeff_Suc real_of_nat_def del: of_nat_Suc)
```
```  2199
```
```  2200 text{*Now at last we can get the derivatives of exp, sin and cos*}
```
```  2201
```
```  2202 lemma DERIV_sin [simp]: "DERIV sin x :> cos(x)"
```
```  2203   unfolding sin_def cos_def
```
```  2204   apply (rule DERIV_cong, rule termdiffs [where K="1 + \<bar>x\<bar>"])
```
```  2205   apply (simp_all add: diffs_sin_coeff diffs_cos_coeff
```
```  2206     summable_minus summable_sin summable_cos)
```
```  2207   done
```
```  2208
```
```  2209 declare DERIV_sin[THEN DERIV_chain2, THEN DERIV_cong, DERIV_intros]
```
```  2210
```
```  2211 lemma DERIV_cos [simp]: "DERIV cos x :> -sin(x)"
```
```  2212   unfolding cos_def sin_def
```
```  2213   apply (rule DERIV_cong, rule termdiffs [where K="1 + \<bar>x\<bar>"])
```
```  2214   apply (simp_all add: diffs_sin_coeff diffs_cos_coeff diffs_minus
```
```  2215     summable_minus summable_sin summable_cos suminf_minus)
```
```  2216   done
```
```  2217
```
```  2218 declare DERIV_cos[THEN DERIV_chain2, THEN DERIV_cong, DERIV_intros]
```
```  2219
```
```  2220 lemma isCont_sin: "isCont sin x"
```
```  2221   by (rule DERIV_sin [THEN DERIV_isCont])
```
```  2222
```
```  2223 lemma isCont_cos: "isCont cos x"
```
```  2224   by (rule DERIV_cos [THEN DERIV_isCont])
```
```  2225
```
```  2226 lemma isCont_sin' [simp]: "isCont f a \<Longrightarrow> isCont (\<lambda>x. sin (f x)) a"
```
```  2227   by (rule isCont_o2 [OF _ isCont_sin])
```
```  2228
```
```  2229 lemma isCont_cos' [simp]: "isCont f a \<Longrightarrow> isCont (\<lambda>x. cos (f x)) a"
```
```  2230   by (rule isCont_o2 [OF _ isCont_cos])
```
```  2231
```
```  2232 lemma tendsto_sin [tendsto_intros]:
```
```  2233   "(f ---> a) F \<Longrightarrow> ((\<lambda>x. sin (f x)) ---> sin a) F"
```
```  2234   by (rule isCont_tendsto_compose [OF isCont_sin])
```
```  2235
```
```  2236 lemma tendsto_cos [tendsto_intros]:
```
```  2237   "(f ---> a) F \<Longrightarrow> ((\<lambda>x. cos (f x)) ---> cos a) F"
```
```  2238   by (rule isCont_tendsto_compose [OF isCont_cos])
```
```  2239
```
```  2240 lemma continuous_sin [continuous_intros]:
```
```  2241   "continuous F f \<Longrightarrow> continuous F (\<lambda>x. sin (f x))"
```
```  2242   unfolding continuous_def by (rule tendsto_sin)
```
```  2243
```
```  2244 lemma continuous_on_sin [continuous_on_intros]:
```
```  2245   "continuous_on s f \<Longrightarrow> continuous_on s (\<lambda>x. sin (f x))"
```
```  2246   unfolding continuous_on_def by (auto intro: tendsto_sin)
```
```  2247
```
```  2248 lemma continuous_cos [continuous_intros]:
```
```  2249   "continuous F f \<Longrightarrow> continuous F (\<lambda>x. cos (f x))"
```
```  2250   unfolding continuous_def by (rule tendsto_cos)
```
```  2251
```
```  2252 lemma continuous_on_cos [continuous_on_intros]:
```
```  2253   "continuous_on s f \<Longrightarrow> continuous_on s (\<lambda>x. cos (f x))"
```
```  2254   unfolding continuous_on_def by (auto intro: tendsto_cos)
```
```  2255
```
```  2256 subsection {* Properties of Sine and Cosine *}
```
```  2257
```
```  2258 lemma sin_zero [simp]: "sin 0 = 0"
```
```  2259   unfolding sin_def sin_coeff_def by (simp add: powser_zero)
```
```  2260
```
```  2261 lemma cos_zero [simp]: "cos 0 = 1"
```
```  2262   unfolding cos_def cos_coeff_def by (simp add: powser_zero)
```
```  2263
```
```  2264 lemma sin_cos_squared_add [simp]: "(sin x)\<^sup>2 + (cos x)\<^sup>2 = 1"
```
```  2265 proof -
```
```  2266   have "\<forall>x. DERIV (\<lambda>x. (sin x)\<^sup>2 + (cos x)\<^sup>2) x :> 0"
```
```  2267     by (auto intro!: DERIV_intros)
```
```  2268   hence "(sin x)\<^sup>2 + (cos x)\<^sup>2 = (sin 0)\<^sup>2 + (cos 0)\<^sup>2"
```
```  2269     by (rule DERIV_isconst_all)
```
```  2270   thus "(sin x)\<^sup>2 + (cos x)\<^sup>2 = 1" by simp
```
```  2271 qed
```
```  2272
```
```  2273 lemma sin_cos_squared_add2 [simp]: "(cos x)\<^sup>2 + (sin x)\<^sup>2 = 1"
```
```  2274   by (subst add_commute, rule sin_cos_squared_add)
```
```  2275
```
```  2276 lemma sin_cos_squared_add3 [simp]: "cos x * cos x + sin x * sin x = 1"
```
```  2277   using sin_cos_squared_add2 [unfolded power2_eq_square] .
```
```  2278
```
```  2279 lemma sin_squared_eq: "(sin x)\<^sup>2 = 1 - (cos x)\<^sup>2"
```
```  2280   unfolding eq_diff_eq by (rule sin_cos_squared_add)
```
```  2281
```
```  2282 lemma cos_squared_eq: "(cos x)\<^sup>2 = 1 - (sin x)\<^sup>2"
```
```  2283   unfolding eq_diff_eq by (rule sin_cos_squared_add2)
```
```  2284
```
```  2285 lemma abs_sin_le_one [simp]: "\<bar>sin x\<bar> \<le> 1"
```
```  2286   by (rule power2_le_imp_le, simp_all add: sin_squared_eq)
```
```  2287
```
```  2288 lemma sin_ge_minus_one [simp]: "-1 \<le> sin x"
```
```  2289   using abs_sin_le_one [of x] unfolding abs_le_iff by simp
```
```  2290
```
```  2291 lemma sin_le_one [simp]: "sin x \<le> 1"
```
```  2292   using abs_sin_le_one [of x] unfolding abs_le_iff by simp
```
```  2293
```
```  2294 lemma abs_cos_le_one [simp]: "\<bar>cos x\<bar> \<le> 1"
```
```  2295   by (rule power2_le_imp_le, simp_all add: cos_squared_eq)
```
```  2296
```
```  2297 lemma cos_ge_minus_one [simp]: "-1 \<le> cos x"
```
```  2298   using abs_cos_le_one [of x] unfolding abs_le_iff by simp
```
```  2299
```
```  2300 lemma cos_le_one [simp]: "cos x \<le> 1"
```
```  2301   using abs_cos_le_one [of x] unfolding abs_le_iff by simp
```
```  2302
```
```  2303 lemma DERIV_fun_pow: "DERIV g x :> m ==>
```
```  2304       DERIV (\<lambda>x. (g x) ^ n) x :> real n * (g x) ^ (n - 1) * m"
```
```  2305   by (auto intro!: DERIV_intros)
```
```  2306
```
```  2307 lemma DERIV_fun_exp:
```
```  2308      "DERIV g x :> m ==> DERIV (\<lambda>x. exp(g x)) x :> exp(g x) * m"
```
```  2309   by (auto intro!: DERIV_intros)
```
```  2310
```
```  2311 lemma DERIV_fun_sin:
```
```  2312      "DERIV g x :> m ==> DERIV (\<lambda>x. sin(g x)) x :> cos(g x) * m"
```
```  2313   by (auto intro!: DERIV_intros)
```
```  2314
```
```  2315 lemma DERIV_fun_cos:
```
```  2316      "DERIV g x :> m ==> DERIV (\<lambda>x. cos(g x)) x :> -sin(g x) * m"
```
```  2317   by (auto intro!: DERIV_intros)
```
```  2318
```
```  2319 lemma sin_cos_add_lemma:
```
```  2320   "(sin (x + y) - (sin x * cos y + cos x * sin y))\<^sup>2 +
```
```  2321     (cos (x + y) - (cos x * cos y - sin x * sin y))\<^sup>2 = 0"
```
```  2322   (is "?f x = 0")
```
```  2323 proof -
```
```  2324   have "\<forall>x. DERIV (\<lambda>x. ?f x) x :> 0"
```
```  2325     by (auto intro!: DERIV_intros simp add: algebra_simps)
```
```  2326   hence "?f x = ?f 0"
```
```  2327     by (rule DERIV_isconst_all)
```
```  2328   thus ?thesis by simp
```
```  2329 qed
```
```  2330
```
```  2331 lemma sin_add: "sin (x + y) = sin x * cos y + cos x * sin y"
```
```  2332   using sin_cos_add_lemma unfolding realpow_two_sum_zero_iff by simp
```
```  2333
```
```  2334 lemma cos_add: "cos (x + y) = cos x * cos y - sin x * sin y"
```
```  2335   using sin_cos_add_lemma unfolding realpow_two_sum_zero_iff by simp
```
```  2336
```
```  2337 lemma sin_cos_minus_lemma:
```
```  2338   "(sin(-x) + sin(x))\<^sup>2 + (cos(-x) - cos(x))\<^sup>2 = 0" (is "?f x = 0")
```
```  2339 proof -
```
```  2340   have "\<forall>x. DERIV (\<lambda>x. ?f x) x :> 0"
```
```  2341     by (auto intro!: DERIV_intros simp add: algebra_simps)
```
```  2342   hence "?f x = ?f 0"
```
```  2343     by (rule DERIV_isconst_all)
```
```  2344   thus ?thesis by simp
```
```  2345 qed
```
```  2346
```
```  2347 lemma sin_minus [simp]: "sin (-x) = -sin(x)"
```
```  2348   using sin_cos_minus_lemma [where x=x] by simp
```
```  2349
```
```  2350 lemma cos_minus [simp]: "cos (-x) = cos(x)"
```
```  2351   using sin_cos_minus_lemma [where x=x] by simp
```
```  2352
```
```  2353 lemma sin_diff: "sin (x - y) = sin x * cos y - cos x * sin y"
```
```  2354   using sin_add [of x "- y"] by simp
```
```  2355
```
```  2356 lemma sin_diff2: "sin (x - y) = cos y * sin x - sin y * cos x"
```
```  2357   by (simp add: sin_diff mult_commute)
```
```  2358
```
```  2359 lemma cos_diff: "cos (x - y) = cos x * cos y + sin x * sin y"
```
```  2360   using cos_add [of x "- y"] by simp
```
```  2361
```
```  2362 lemma cos_diff2: "cos (x - y) = cos y * cos x + sin y * sin x"
```
```  2363   by (simp add: cos_diff mult_commute)
```
```  2364
```
```  2365 lemma sin_double [simp]: "sin(2 * x) = 2* sin x * cos x"
```
```  2366   using sin_add [where x=x and y=x] by simp
```
```  2367
```
```  2368 lemma cos_double: "cos(2* x) = ((cos x)\<^sup>2) - ((sin x)\<^sup>2)"
```
```  2369   using cos_add [where x=x and y=x]
```
```  2370   by (simp add: power2_eq_square)
```
```  2371
```
```  2372
```
```  2373 subsection {* The Constant Pi *}
```
```  2374
```
```  2375 definition pi :: real
```
```  2376   where "pi = 2 * (THE x. 0 \<le> (x::real) & x \<le> 2 & cos x = 0)"
```
```  2377
```
```  2378 text{*Show that there's a least positive @{term x} with @{term "cos(x) = 0"};
```
```  2379    hence define pi.*}
```
```  2380
```
```  2381 lemma sin_paired:
```
```  2382   "(\<lambda>n. -1 ^ n /(real (fact (2 * n + 1))) * x ^ (2 * n + 1)) sums  sin x"
```
```  2383 proof -
```
```  2384   have "(\<lambda>n. \<Sum>k = n * 2..<n * 2 + 2. sin_coeff k * x ^ k) sums sin x"
```
```  2385     by (rule sin_converges [THEN sums_group], simp)
```
```  2386   thus ?thesis unfolding One_nat_def sin_coeff_def by (simp add: mult_ac)
```
```  2387 qed
```
```  2388
```
```  2389 lemma sin_gt_zero:
```
```  2390   assumes "0 < x" and "x < 2"
```
```  2391   shows "0 < sin x"
```
```  2392 proof -
```
```  2393   let ?f = "\<lambda>n. \<Sum>k = n*2..<n*2+2. -1 ^ k / real (fact (2*k+1)) * x^(2*k+1)"
```
```  2394   have pos: "\<forall>n. 0 < ?f n"
```
```  2395   proof
```
```  2396     fix n :: nat
```
```  2397     let ?k2 = "real (Suc (Suc (4 * n)))"
```
```  2398     let ?k3 = "real (Suc (Suc (Suc (4 * n))))"
```
```  2399     have "x * x < ?k2 * ?k3"
```
```  2400       using assms by (intro mult_strict_mono', simp_all)
```
```  2401     hence "x * x * x * x ^ (n * 4) < ?k2 * ?k3 * x * x ^ (n * 4)"
```
```  2402       by (intro mult_strict_right_mono zero_less_power `0 < x`)
```
```  2403     thus "0 < ?f n"
```
```  2404       by (simp del: mult_Suc,
```
```  2405         simp add: less_divide_eq mult_pos_pos field_simps del: mult_Suc)
```
```  2406   qed
```
```  2407   have sums: "?f sums sin x"
```
```  2408     by (rule sin_paired [THEN sums_group], simp)
```
```  2409   show "0 < sin x"
```
```  2410     unfolding sums_unique [OF sums]
```
```  2411     using sums_summable [OF sums] pos
```
```  2412     by (rule suminf_gt_zero)
```
```  2413 qed
```
```  2414
```
```  2415 lemma cos_double_less_one: "0 < x \<Longrightarrow> x < 2 \<Longrightarrow> cos (2 * x) < 1"
```
```  2416   using sin_gt_zero [where x = x] by (auto simp add: cos_squared_eq cos_double)
```
```  2417
```
```  2418 lemma cos_paired: "(\<lambda>n. -1 ^ n /(real (fact (2 * n))) * x ^ (2 * n)) sums cos x"
```
```  2419 proof -
```
```  2420   have "(\<lambda>n. \<Sum>k = n * 2..<n * 2 + 2. cos_coeff k * x ^ k) sums cos x"
```
```  2421     by (rule cos_converges [THEN sums_group], simp)
```
```  2422   thus ?thesis unfolding cos_coeff_def by (simp add: mult_ac)
```
```  2423 qed
```
```  2424
```
```  2425 lemma real_mult_inverse_cancel:
```
```  2426      "[|(0::real) < x; 0 < x1; x1 * y < x * u |]
```
```  2427       ==> inverse x * y < inverse x1 * u"
```
```  2428   by (metis field_divide_inverse mult_commute mult_assoc pos_divide_less_eq pos_less_divide_eq)
```
```  2429
```
```  2430 lemma real_mult_inverse_cancel2:
```
```  2431      "[|(0::real) < x;0 < x1; x1 * y < x * u |] ==> y * inverse x < u * inverse x1"
```
```  2432   by (auto dest: real_mult_inverse_cancel simp add: mult_ac)
```
```  2433
```
```  2434 lemmas realpow_num_eq_if = power_eq_if
```
```  2435
```
```  2436 lemma cos_two_less_zero [simp]:
```
```  2437   "cos 2 < 0"
```
```  2438 proof -
```
```  2439   note fact_Suc [simp del]
```
```  2440   from cos_paired
```
```  2441   have "(\<lambda>n. - (-1 ^ n / real (fact (2 * n)) * 2 ^ (2 * n))) sums - cos 2"
```
```  2442     by (rule sums_minus)
```
```  2443   then have *: "(\<lambda>n. - (-1 ^ n * 2 ^ (2 * n) / real (fact (2 * n)))) sums - cos 2"
```
```  2444     by simp
```
```  2445   then have **: "summable (\<lambda>n. - (-1 ^ n * 2 ^ (2 * n) / real (fact (2 * n))))"
```
```  2446     by (rule sums_summable)
```
```  2447   have "0 < (\<Sum>n = 0..<Suc (Suc (Suc 0)). - (-1 ^ n * 2 ^ (2 * n) / real (fact (2 * n))))"
```
```  2448     by (simp add: fact_num_eq_if_nat realpow_num_eq_if)
```
```  2449   moreover have "(\<Sum>n = 0..<Suc (Suc (Suc 0)). - (-1 ^ n  * 2 ^ (2 * n) / real (fact (2 * n))))
```
```  2450     < (\<Sum>n. - (-1 ^ n * 2 ^ (2 * n) / real (fact (2 * n))))"
```
```  2451   proof -
```
```  2452     { fix d
```
```  2453       have "4 * real (fact (Suc (Suc (Suc (Suc (Suc (Suc (4 * d))))))))
```
```  2454        < real (Suc (Suc (Suc (Suc (Suc (Suc (Suc (Suc (4 * d)))))))) *
```
```  2455            fact (Suc (Suc (Suc (Suc (Suc (Suc (Suc (4 * d)))))))))"
```
```  2456         by (simp only: real_of_nat_mult) (auto intro!: mult_strict_mono fact_less_mono_nat)
```
```  2457       then have "4 * real (fact (Suc (Suc (Suc (Suc (Suc (Suc (4 * d))))))))
```
```  2458         < real (fact (Suc (Suc (Suc (Suc (Suc (Suc (Suc (Suc (4 * d))))))))))"
```
```  2459         by (simp only: fact_Suc [of "Suc (Suc (Suc (Suc (Suc (Suc (Suc (4 * d)))))))"])
```
```  2460       then have "4 * inverse (real (fact (Suc (Suc (Suc (Suc (Suc (Suc (Suc (Suc (4 * d)))))))))))
```
```  2461         < inverse (real (fact (Suc (Suc (Suc (Suc (Suc (Suc (4 * d)))))))))"
```
```  2462         by (simp add: inverse_eq_divide less_divide_eq)
```
```  2463     }
```
```  2464     note *** = this
```
```  2465     have [simp]: "\<And>x y::real. 0 < x - y \<longleftrightarrow> y < x" by arith
```
```  2466     from ** show ?thesis by (rule sumr_pos_lt_pair)
```
```  2467       (simp add: divide_inverse mult_assoc [symmetric] ***)
```
```  2468   qed
```
```  2469   ultimately have "0 < (\<Sum>n. - (-1 ^ n * 2 ^ (2 * n) / real (fact (2 * n))))"
```
```  2470     by (rule order_less_trans)
```
```  2471   moreover from * have "- cos 2 = (\<Sum>n. - (-1 ^ n * 2 ^ (2 * n) / real (fact (2 * n))))"
```
```  2472     by (rule sums_unique)
```
```  2473   ultimately have "0 < - cos 2" by simp
```
```  2474   then show ?thesis by simp
```
```  2475 qed
```
```  2476
```
```  2477 lemmas cos_two_neq_zero [simp] = cos_two_less_zero [THEN less_imp_neq]
```
```  2478 lemmas cos_two_le_zero [simp] = cos_two_less_zero [THEN order_less_imp_le]
```
```  2479
```
```  2480 lemma cos_is_zero: "EX! x. 0 \<le> x & x \<le> 2 \<and> cos x = 0"
```
```  2481 proof (rule ex_ex1I)
```
```  2482   show "\<exists>x. 0 \<le> x & x \<le> 2 & cos x = 0"
```
```  2483     by (rule IVT2, simp_all)
```
```  2484 next
```
```  2485   fix x y
```
```  2486   assume x: "0 \<le> x \<and> x \<le> 2 \<and> cos x = 0"
```
```  2487   assume y: "0 \<le> y \<and> y \<le> 2 \<and> cos y = 0"
```
```  2488   have [simp]: "\<forall>x. cos differentiable (at x)"
```
```  2489     unfolding real_differentiable_def by (auto intro: DERIV_cos)
```
```  2490   from x y show "x = y"
```
```  2491     apply (cut_tac less_linear [of x y], auto)
```
```  2492     apply (drule_tac f = cos in Rolle)
```
```  2493     apply (drule_tac [5] f = cos in Rolle)
```
```  2494     apply (auto dest!: DERIV_cos [THEN DERIV_unique])
```
```  2495     apply (metis order_less_le_trans less_le sin_gt_zero)
```
```  2496     apply (metis order_less_le_trans less_le sin_gt_zero)
```
```  2497     done
```
```  2498 qed
```
```  2499
```
```  2500 lemma pi_half: "pi/2 = (THE x. 0 \<le> x & x \<le> 2 & cos x = 0)"
```
```  2501   by (simp add: pi_def)
```
```  2502
```
```  2503 lemma cos_pi_half [simp]: "cos (pi / 2) = 0"
```
```  2504   by (simp add: pi_half cos_is_zero [THEN theI'])
```
```  2505
```
```  2506 lemma pi_half_gt_zero [simp]: "0 < pi / 2"
```
```  2507   apply (rule order_le_neq_trans)
```
```  2508   apply (simp add: pi_half cos_is_zero [THEN theI'])
```
```  2509   apply (metis cos_pi_half cos_zero zero_neq_one)
```
```  2510   done
```
```  2511
```
```  2512 lemmas pi_half_neq_zero [simp] = pi_half_gt_zero [THEN less_imp_neq, symmetric]
```
```  2513 lemmas pi_half_ge_zero [simp] = pi_half_gt_zero [THEN order_less_imp_le]
```
```  2514
```
```  2515 lemma pi_half_less_two [simp]: "pi / 2 < 2"
```
```  2516   apply (rule order_le_neq_trans)
```
```  2517   apply (simp add: pi_half cos_is_zero [THEN theI'])
```
```  2518   apply (metis cos_pi_half cos_two_neq_zero)
```
```  2519   done
```
```  2520
```
```  2521 lemmas pi_half_neq_two [simp] = pi_half_less_two [THEN less_imp_neq]
```
```  2522 lemmas pi_half_le_two [simp] =  pi_half_less_two [THEN order_less_imp_le]
```
```  2523
```
```  2524 lemma pi_gt_zero [simp]: "0 < pi"
```
```  2525   using pi_half_gt_zero by simp
```
```  2526
```
```  2527 lemma pi_ge_zero [simp]: "0 \<le> pi"
```
```  2528   by (rule pi_gt_zero [THEN order_less_imp_le])
```
```  2529
```
```  2530 lemma pi_neq_zero [simp]: "pi \<noteq> 0"
```
```  2531   by (rule pi_gt_zero [THEN less_imp_neq, symmetric])
```
```  2532
```
```  2533 lemma pi_not_less_zero [simp]: "\<not> pi < 0"
```
```  2534   by (simp add: linorder_not_less)
```
```  2535
```
```  2536 lemma minus_pi_half_less_zero: "-(pi/2) < 0"
```
```  2537   by simp
```
```  2538
```
```  2539 lemma m2pi_less_pi: "- (2 * pi) < pi"
```
```  2540   by simp
```
```  2541
```
```  2542 lemma sin_pi_half [simp]: "sin(pi/2) = 1"
```
```  2543   using sin_cos_squared_add2 [where x = "pi/2"]
```
```  2544   using sin_gt_zero [OF pi_half_gt_zero pi_half_less_two]
```
```  2545   by (simp add: power2_eq_1_iff)
```
```  2546
```
```  2547 lemma cos_pi [simp]: "cos pi = -1"
```
```  2548   using cos_add [where x = "pi/2" and y = "pi/2"] by simp
```
```  2549
```
```  2550 lemma sin_pi [simp]: "sin pi = 0"
```
```  2551   using sin_add [where x = "pi/2" and y = "pi/2"] by simp
```
```  2552
```
```  2553 lemma sin_cos_eq: "sin x = cos (pi/2 - x)"
```
```  2554   by (simp add: cos_diff)
```
```  2555
```
```  2556 lemma minus_sin_cos_eq: "-sin x = cos (x + pi/2)"
```
```  2557   by (simp add: cos_add)
```
```  2558
```
```  2559 lemma cos_sin_eq: "cos x = sin (pi/2 - x)"
```
```  2560   by (simp add: sin_diff)
```
```  2561
```
```  2562 lemma sin_periodic_pi [simp]: "sin (x + pi) = - sin x"
```
```  2563   by (simp add: sin_add)
```
```  2564
```
```  2565 lemma sin_periodic_pi2 [simp]: "sin (pi + x) = - sin x"
```
```  2566   by (simp add: sin_add)
```
```  2567
```
```  2568 lemma cos_periodic_pi [simp]: "cos (x + pi) = - cos x"
```
```  2569   by (simp add: cos_add)
```
```  2570
```
```  2571 lemma sin_periodic [simp]: "sin (x + 2*pi) = sin x"
```
```  2572   by (simp add: sin_add cos_double)
```
```  2573
```
```  2574 lemma cos_periodic [simp]: "cos (x + 2*pi) = cos x"
```
```  2575   by (simp add: cos_add cos_double)
```
```  2576
```
```  2577 lemma cos_npi [simp]: "cos (real n * pi) = -1 ^ n"
```
```  2578   by (induct n) (auto simp add: real_of_nat_Suc distrib_right)
```
```  2579
```
```  2580 lemma cos_npi2 [simp]: "cos (pi * real n) = -1 ^ n"
```
```  2581   by (metis cos_npi mult_commute)
```
```  2582
```
```  2583 lemma sin_npi [simp]: "sin (real (n::nat) * pi) = 0"
```
```  2584   by (induct n) (auto simp add: real_of_nat_Suc distrib_right)
```
```  2585
```
```  2586 lemma sin_npi2 [simp]: "sin (pi * real (n::nat)) = 0"
```
```  2587   by (simp add: mult_commute [of pi])
```
```  2588
```
```  2589 lemma cos_two_pi [simp]: "cos (2 * pi) = 1"
```
```  2590   by (simp add: cos_double)
```
```  2591
```
```  2592 lemma sin_two_pi [simp]: "sin (2 * pi) = 0"
```
```  2593   by simp
```
```  2594
```
```  2595 lemma sin_gt_zero2: "[| 0 < x; x < pi/2 |] ==> 0 < sin x"
```
```  2596   by (metis sin_gt_zero order_less_trans pi_half_less_two)
```
```  2597
```
```  2598 lemma sin_less_zero:
```
```  2599   assumes "- pi/2 < x" and "x < 0"
```
```  2600   shows "sin x < 0"
```
```  2601 proof -
```
```  2602   have "0 < sin (- x)" using assms by (simp only: sin_gt_zero2)
```
```  2603   thus ?thesis by simp
```
```  2604 qed
```
```  2605
```
```  2606 lemma pi_less_4: "pi < 4"
```
```  2607   using pi_half_less_two by auto
```
```  2608
```
```  2609 lemma cos_gt_zero: "[| 0 < x; x < pi/2 |] ==> 0 < cos x"
```
```  2610   apply (cut_tac pi_less_4)
```
```  2611   apply (cut_tac f = cos and a = 0 and b = x and y = 0 in IVT2_objl, safe, simp_all)
```
```  2612   apply (cut_tac cos_is_zero, safe)
```
```  2613   apply (rename_tac y z)
```
```  2614   apply (drule_tac x = y in spec)
```
```  2615   apply (drule_tac x = "pi/2" in spec, simp)
```
```  2616   done
```
```  2617
```
```  2618 lemma cos_gt_zero_pi: "[| -(pi/2) < x; x < pi/2 |] ==> 0 < cos x"
```
```  2619   apply (rule_tac x = x and y = 0 in linorder_cases)
```
```  2620   apply (metis cos_gt_zero cos_minus minus_less_iff neg_0_less_iff_less)
```
```  2621   apply (auto intro: cos_gt_zero)
```
```  2622   done
```
```  2623
```
```  2624 lemma cos_ge_zero: "[| -(pi/2) \<le> x; x \<le> pi/2 |] ==> 0 \<le> cos x"
```
```  2625   apply (auto simp add: order_le_less cos_gt_zero_pi)
```
```  2626   apply (subgoal_tac "x = pi/2", auto)
```
```  2627   done
```
```  2628
```
```  2629 lemma sin_gt_zero_pi: "[| 0 < x; x < pi  |] ==> 0 < sin x"
```
```  2630   by (simp add: sin_cos_eq cos_gt_zero_pi)
```
```  2631
```
```  2632 lemma pi_ge_two: "2 \<le> pi"
```
```  2633 proof (rule ccontr)
```
```  2634   assume "\<not> 2 \<le> pi" hence "pi < 2" by auto
```
```  2635   have "\<exists>y > pi. y < 2 \<and> y < 2 * pi"
```
```  2636   proof (cases "2 < 2 * pi")
```
```  2637     case True with dense[OF `pi < 2`] show ?thesis by auto
```
```  2638   next
```
```  2639     case False have "pi < 2 * pi" by auto
```
```  2640     from dense[OF this] and False show ?thesis by auto
```
```  2641   qed
```
```  2642   then obtain y where "pi < y" and "y < 2" and "y < 2 * pi" by blast
```
```  2643   hence "0 < sin y" using sin_gt_zero by auto
```
```  2644   moreover
```
```  2645   have "sin y < 0" using sin_gt_zero_pi[of "y - pi"] `pi < y` and `y < 2 * pi` sin_periodic_pi[of "y - pi"] by auto
```
```  2646   ultimately show False by auto
```
```  2647 qed
```
```  2648
```
```  2649 lemma sin_ge_zero: "[| 0 \<le> x; x \<le> pi |] ==> 0 \<le> sin x"
```
```  2650   by (auto simp add: order_le_less sin_gt_zero_pi)
```
```  2651
```
```  2652 text {* FIXME: This proof is almost identical to lemma @{text cos_is_zero}.
```
```  2653   It should be possible to factor out some of the common parts. *}
```
```  2654
```
```  2655 lemma cos_total: "[| -1 \<le> y; y \<le> 1 |] ==> EX! x. 0 \<le> x & x \<le> pi & (cos x = y)"
```
```  2656 proof (rule ex_ex1I)
```
```  2657   assume y: "-1 \<le> y" "y \<le> 1"
```
```  2658   show "\<exists>x. 0 \<le> x & x \<le> pi & cos x = y"
```
```  2659     by (rule IVT2, simp_all add: y)
```
```  2660 next
```
```  2661   fix a b
```
```  2662   assume a: "0 \<le> a \<and> a \<le> pi \<and> cos a = y"
```
```  2663   assume b: "0 \<le> b \<and> b \<le> pi \<and> cos b = y"
```
```  2664   have [simp]: "\<forall>x. cos differentiable (at x)"
```
```  2665     unfolding real_differentiable_def by (auto intro: DERIV_cos)
```
```  2666   from a b show "a = b"
```
```  2667     apply (cut_tac less_linear [of a b], auto)
```
```  2668     apply (drule_tac f = cos in Rolle)
```
```  2669     apply (drule_tac [5] f = cos in Rolle)
```
```  2670     apply (auto dest!: DERIV_cos [THEN DERIV_unique])
```
```  2671     apply (metis order_less_le_trans less_le sin_gt_zero_pi)
```
```  2672     apply (metis order_less_le_trans less_le sin_gt_zero_pi)
```
```  2673     done
```
```  2674 qed
```
```  2675
```
```  2676 lemma sin_total:
```
```  2677      "[| -1 \<le> y; y \<le> 1 |] ==> EX! x. -(pi/2) \<le> x & x \<le> pi/2 & (sin x = y)"
```
```  2678 apply (rule ccontr)
```
```  2679 apply (subgoal_tac "\<forall>x. (- (pi/2) \<le> x & x \<le> pi/2 & (sin x = y)) = (0 \<le> (x + pi/2) & (x + pi/2) \<le> pi & (cos (x + pi/2) = -y))")
```
```  2680 apply (erule contrapos_np)
```
```  2681 apply simp
```
```  2682 apply (cut_tac y="-y" in cos_total, simp) apply simp
```
```  2683 apply (erule ex1E)
```
```  2684 apply (rule_tac a = "x - (pi/2)" in ex1I)
```
```  2685 apply (simp (no_asm) add: add_assoc)
```
```  2686 apply (rotate_tac 3)
```
```  2687 apply (drule_tac x = "xa + pi/2" in spec, safe, simp_all add: cos_add)
```
```  2688 done
```
```  2689
```
```  2690 lemma reals_Archimedean4:
```
```  2691      "[| 0 < y; 0 \<le> x |] ==> \<exists>n. real n * y \<le> x & x < real (Suc n) * y"
```
```  2692 apply (auto dest!: reals_Archimedean3)
```
```  2693 apply (drule_tac x = x in spec, clarify)
```
```  2694 apply (subgoal_tac "x < real(LEAST m::nat. x < real m * y) * y")
```
```  2695  prefer 2 apply (erule LeastI)
```
```  2696 apply (case_tac "LEAST m::nat. x < real m * y", simp)
```
```  2697 apply (rename_tac m)
```
```  2698 apply (subgoal_tac "~ x < real m * y")
```
```  2699  prefer 2 apply (rule not_less_Least, simp, force)
```
```  2700 done
```
```  2701
```
```  2702 (* Pre Isabelle99-2 proof was simpler- numerals arithmetic
```
```  2703    now causes some unwanted re-arrangements of literals!   *)
```
```  2704 lemma cos_zero_lemma:
```
```  2705      "[| 0 \<le> x; cos x = 0 |] ==>
```
```  2706       \<exists>n::nat. ~even n & x = real n * (pi/2)"
```
```  2707 apply (drule pi_gt_zero [THEN reals_Archimedean4], safe)
```
```  2708 apply (subgoal_tac "0 \<le> x - real n * pi &
```
```  2709                     (x - real n * pi) \<le> pi & (cos (x - real n * pi) = 0) ")
```
```  2710 apply (auto simp add: algebra_simps real_of_nat_Suc)
```
```  2711  prefer 2 apply (simp add: cos_diff)
```
```  2712 apply (simp add: cos_diff)
```
```  2713 apply (subgoal_tac "EX! x. 0 \<le> x & x \<le> pi & cos x = 0")
```
```  2714 apply (rule_tac [2] cos_total, safe)
```
```  2715 apply (drule_tac x = "x - real n * pi" in spec)
```
```  2716 apply (drule_tac x = "pi/2" in spec)
```
```  2717 apply (simp add: cos_diff)
```
```  2718 apply (rule_tac x = "Suc (2 * n)" in exI)
```
```  2719 apply (simp add: real_of_nat_Suc algebra_simps, auto)
```
```  2720 done
```
```  2721
```
```  2722 lemma sin_zero_lemma:
```
```  2723      "[| 0 \<le> x; sin x = 0 |] ==>
```
```  2724       \<exists>n::nat. even n & x = real n * (pi/2)"
```
```  2725 apply (subgoal_tac "\<exists>n::nat. ~ even n & x + pi/2 = real n * (pi/2) ")
```
```  2726  apply (clarify, rule_tac x = "n - 1" in exI)
```
```  2727  apply (force simp add: odd_Suc_mult_two_ex real_of_nat_Suc distrib_right)
```
```  2728 apply (rule cos_zero_lemma)
```
```  2729 apply (simp_all add: cos_add)
```
```  2730 done
```
```  2731
```
```  2732
```
```  2733 lemma cos_zero_iff:
```
```  2734      "(cos x = 0) =
```
```  2735       ((\<exists>n::nat. ~even n & (x = real n * (pi/2))) |
```
```  2736        (\<exists>n::nat. ~even n & (x = -(real n * (pi/2)))))"
```
```  2737 apply (rule iffI)
```
```  2738 apply (cut_tac linorder_linear [of 0 x], safe)
```
```  2739 apply (drule cos_zero_lemma, assumption+)
```
```  2740 apply (cut_tac x="-x" in cos_zero_lemma, simp, simp)
```
```  2741 apply (force simp add: minus_equation_iff [of x])
```
```  2742 apply (auto simp only: odd_Suc_mult_two_ex real_of_nat_Suc distrib_right)
```
```  2743 apply (auto simp add: cos_diff cos_add)
```
```  2744 done
```
```  2745
```
```  2746 (* ditto: but to a lesser extent *)
```
```  2747 lemma sin_zero_iff:
```
```  2748      "(sin x = 0) =
```
```  2749       ((\<exists>n::nat. even n & (x = real n * (pi/2))) |
```
```  2750        (\<exists>n::nat. even n & (x = -(real n * (pi/2)))))"
```
```  2751 apply (rule iffI)
```
```  2752 apply (cut_tac linorder_linear [of 0 x], safe)
```
```  2753 apply (drule sin_zero_lemma, assumption+)
```
```  2754 apply (cut_tac x="-x" in sin_zero_lemma, simp, simp, safe)
```
```  2755 apply (force simp add: minus_equation_iff [of x])
```
```  2756 apply (auto simp add: even_mult_two_ex)
```
```  2757 done
```
```  2758
```
```  2759 lemma cos_monotone_0_pi:
```
```  2760   assumes "0 \<le> y" and "y < x" and "x \<le> pi"
```
```  2761   shows "cos x < cos y"
```
```  2762 proof -
```
```  2763   have "- (x - y) < 0" using assms by auto
```
```  2764
```
```  2765   from MVT2[OF `y < x` DERIV_cos[THEN impI, THEN allI]]
```
```  2766   obtain z where "y < z" and "z < x" and cos_diff: "cos x - cos y = (x - y) * - sin z"
```
```  2767     by auto
```
```  2768   hence "0 < z" and "z < pi" using assms by auto
```
```  2769   hence "0 < sin z" using sin_gt_zero_pi by auto
```
```  2770   hence "cos x - cos y < 0"
```
```  2771     unfolding cos_diff minus_mult_commute[symmetric]
```
```  2772     using `- (x - y) < 0` by (rule mult_pos_neg2)
```
```  2773   thus ?thesis by auto
```
```  2774 qed
```
```  2775
```
```  2776 lemma cos_monotone_0_pi':
```
```  2777   assumes "0 \<le> y" and "y \<le> x" and "x \<le> pi"
```
```  2778   shows "cos x \<le> cos y"
```
```  2779 proof (cases "y < x")
```
```  2780   case True
```
```  2781   show ?thesis
```
```  2782     using cos_monotone_0_pi[OF `0 \<le> y` True `x \<le> pi`] by auto
```
```  2783 next
```
```  2784   case False
```
```  2785   hence "y = x" using `y \<le> x` by auto
```
```  2786   thus ?thesis by auto
```
```  2787 qed
```
```  2788
```
```  2789 lemma cos_monotone_minus_pi_0:
```
```  2790   assumes "-pi \<le> y" and "y < x" and "x \<le> 0"
```
```  2791   shows "cos y < cos x"
```
```  2792 proof -
```
```  2793   have "0 \<le> -x" and "-x < -y" and "-y \<le> pi"
```
```  2794     using assms by auto
```
```  2795   from cos_monotone_0_pi[OF this] show ?thesis
```
```  2796     unfolding cos_minus .
```
```  2797 qed
```
```  2798
```
```  2799 lemma cos_monotone_minus_pi_0':
```
```  2800   assumes "-pi \<le> y" and "y \<le> x" and "x \<le> 0"
```
```  2801   shows "cos y \<le> cos x"
```
```  2802 proof (cases "y < x")
```
```  2803   case True
```
```  2804   show ?thesis using cos_monotone_minus_pi_0[OF `-pi \<le> y` True `x \<le> 0`]
```
```  2805     by auto
```
```  2806 next
```
```  2807   case False
```
```  2808   hence "y = x" using `y \<le> x` by auto
```
```  2809   thus ?thesis by auto
```
```  2810 qed
```
```  2811
```
```  2812 lemma sin_monotone_2pi':
```
```  2813   assumes "- (pi / 2) \<le> y" and "y \<le> x" and "x \<le> pi / 2"
```
```  2814   shows "sin y \<le> sin x"
```
```  2815 proof -
```
```  2816   have "0 \<le> y + pi / 2" and "y + pi / 2 \<le> x + pi / 2" and "x + pi /2 \<le> pi"
```
```  2817     using pi_ge_two and assms by auto
```
```  2818   from cos_monotone_0_pi'[OF this] show ?thesis
```
```  2819     unfolding minus_sin_cos_eq[symmetric] by auto
```
```  2820 qed
```
```  2821
```
```  2822
```
```  2823 subsection {* Tangent *}
```
```  2824
```
```  2825 definition tan :: "real \<Rightarrow> real"
```
```  2826   where "tan = (\<lambda>x. sin x / cos x)"
```
```  2827
```
```  2828 lemma tan_zero [simp]: "tan 0 = 0"
```
```  2829   by (simp add: tan_def)
```
```  2830
```
```  2831 lemma tan_pi [simp]: "tan pi = 0"
```
```  2832   by (simp add: tan_def)
```
```  2833
```
```  2834 lemma tan_npi [simp]: "tan (real (n::nat) * pi) = 0"
```
```  2835   by (simp add: tan_def)
```
```  2836
```
```  2837 lemma tan_minus [simp]: "tan (-x) = - tan x"
```
```  2838   by (simp add: tan_def)
```
```  2839
```
```  2840 lemma tan_periodic [simp]: "tan (x + 2*pi) = tan x"
```
```  2841   by (simp add: tan_def)
```
```  2842
```
```  2843 lemma lemma_tan_add1:
```
```  2844   "\<lbrakk>cos x \<noteq> 0; cos y \<noteq> 0\<rbrakk> \<Longrightarrow> 1 - tan x * tan y = cos (x + y)/(cos x * cos y)"
```
```  2845   by (simp add: tan_def cos_add field_simps)
```
```  2846
```
```  2847 lemma add_tan_eq:
```
```  2848   "\<lbrakk>cos x \<noteq> 0; cos y \<noteq> 0\<rbrakk> \<Longrightarrow> tan x + tan y = sin(x + y)/(cos x * cos y)"
```
```  2849   by (simp add: tan_def sin_add field_simps)
```
```  2850
```
```  2851 lemma tan_add:
```
```  2852      "[| cos x \<noteq> 0; cos y \<noteq> 0; cos (x + y) \<noteq> 0 |]
```
```  2853       ==> tan(x + y) = (tan(x) + tan(y))/(1 - tan(x) * tan(y))"
```
```  2854   by (simp add: add_tan_eq lemma_tan_add1, simp add: tan_def)
```
```  2855
```
```  2856 lemma tan_double:
```
```  2857      "[| cos x \<noteq> 0; cos (2 * x) \<noteq> 0 |]
```
```  2858       ==> tan (2 * x) = (2 * tan x) / (1 - (tan x)\<^sup>2)"
```
```  2859   using tan_add [of x x] by (simp add: power2_eq_square)
```
```  2860
```
```  2861 lemma tan_gt_zero: "[| 0 < x; x < pi/2 |] ==> 0 < tan x"
```
```  2862   by (simp add: tan_def zero_less_divide_iff sin_gt_zero2 cos_gt_zero_pi)
```
```  2863
```
```  2864 lemma tan_less_zero:
```
```  2865   assumes lb: "- pi/2 < x" and "x < 0"
```
```  2866   shows "tan x < 0"
```
```  2867 proof -
```
```  2868   have "0 < tan (- x)" using assms by (simp only: tan_gt_zero)
```
```  2869   thus ?thesis by simp
```
```  2870 qed
```
```  2871
```
```  2872 lemma tan_half: "tan x = sin (2 * x) / (cos (2 * x) + 1)"
```
```  2873   unfolding tan_def sin_double cos_double sin_squared_eq
```
```  2874   by (simp add: power2_eq_square)
```
```  2875
```
```  2876 lemma DERIV_tan [simp]: "cos x \<noteq> 0 \<Longrightarrow> DERIV tan x :> inverse ((cos x)\<^sup>2)"
```
```  2877   unfolding tan_def
```
```  2878   by (auto intro!: DERIV_intros, simp add: divide_inverse power2_eq_square)
```
```  2879
```
```  2880 lemma isCont_tan: "cos x \<noteq> 0 \<Longrightarrow> isCont tan x"
```
```  2881   by (rule DERIV_tan [THEN DERIV_isCont])
```
```  2882
```
```  2883 lemma isCont_tan' [simp]:
```
```  2884   "\<lbrakk>isCont f a; cos (f a) \<noteq> 0\<rbrakk> \<Longrightarrow> isCont (\<lambda>x. tan (f x)) a"
```
```  2885   by (rule isCont_o2 [OF _ isCont_tan])
```
```  2886
```
```  2887 lemma tendsto_tan [tendsto_intros]:
```
```  2888   "\<lbrakk>(f ---> a) F; cos a \<noteq> 0\<rbrakk> \<Longrightarrow> ((\<lambda>x. tan (f x)) ---> tan a) F"
```
```  2889   by (rule isCont_tendsto_compose [OF isCont_tan])
```
```  2890
```
```  2891 lemma continuous_tan:
```
```  2892   "continuous F f \<Longrightarrow> cos (f (Lim F (\<lambda>x. x))) \<noteq> 0 \<Longrightarrow> continuous F (\<lambda>x. tan (f x))"
```
```  2893   unfolding continuous_def by (rule tendsto_tan)
```
```  2894
```
```  2895 lemma isCont_tan'' [continuous_intros]:
```
```  2896   "continuous (at x) f \<Longrightarrow> cos (f x) \<noteq> 0 \<Longrightarrow> continuous (at x) (\<lambda>x. tan (f x))"
```
```  2897   unfolding continuous_at by (rule tendsto_tan)
```
```  2898
```
```  2899 lemma continuous_within_tan [continuous_intros]:
```
```  2900   "continuous (at x within s) f \<Longrightarrow> cos (f x) \<noteq> 0 \<Longrightarrow> continuous (at x within s) (\<lambda>x. tan (f x))"
```
```  2901   unfolding continuous_within by (rule tendsto_tan)
```
```  2902
```
```  2903 lemma continuous_on_tan [continuous_on_intros]:
```
```  2904   "continuous_on s f \<Longrightarrow> (\<forall>x\<in>s. cos (f x) \<noteq> 0) \<Longrightarrow> continuous_on s (\<lambda>x. tan (f x))"
```
```  2905   unfolding continuous_on_def by (auto intro: tendsto_tan)
```
```  2906
```
```  2907 lemma LIM_cos_div_sin: "(\<lambda>x. cos(x)/sin(x)) -- pi/2 --> 0"
```
```  2908   by (rule LIM_cong_limit, (rule tendsto_intros)+, simp_all)
```
```  2909
```
```  2910 lemma lemma_tan_total: "0 < y ==> \<exists>x. 0 < x & x < pi/2 & y < tan x"
```
```  2911   apply (cut_tac LIM_cos_div_sin)
```
```  2912   apply (simp only: LIM_eq)
```
```  2913   apply (drule_tac x = "inverse y" in spec, safe, force)
```
```  2914   apply (drule_tac ?d1.0 = s in pi_half_gt_zero [THEN [2] real_lbound_gt_zero], safe)
```
```  2915   apply (rule_tac x = "(pi/2) - e" in exI)
```
```  2916   apply (simp (no_asm_simp))
```
```  2917   apply (drule_tac x = "(pi/2) - e" in spec)
```
```  2918   apply (auto simp add: tan_def sin_diff cos_diff)
```
```  2919   apply (rule inverse_less_iff_less [THEN iffD1])
```
```  2920   apply (auto simp add: divide_inverse)
```
```  2921   apply (rule mult_pos_pos)
```
```  2922   apply (subgoal_tac [3] "0 < sin e & 0 < cos e")
```
```  2923   apply (auto intro: cos_gt_zero sin_gt_zero2 simp add: mult_commute)
```
```  2924   done
```
```  2925
```
```  2926 lemma tan_total_pos: "0 \<le> y ==> \<exists>x. 0 \<le> x & x < pi/2 & tan x = y"
```
```  2927   apply (frule order_le_imp_less_or_eq, safe)
```
```  2928    prefer 2 apply force
```
```  2929   apply (drule lemma_tan_total, safe)
```
```  2930   apply (cut_tac f = tan and a = 0 and b = x and y = y in IVT_objl)
```
```  2931   apply (auto intro!: DERIV_tan [THEN DERIV_isCont])
```
```  2932   apply (drule_tac y = xa in order_le_imp_less_or_eq)
```
```  2933   apply (auto dest: cos_gt_zero)
```
```  2934   done
```
```  2935
```
```  2936 lemma lemma_tan_total1: "\<exists>x. -(pi/2) < x & x < (pi/2) & tan x = y"
```
```  2937   apply (cut_tac linorder_linear [of 0 y], safe)
```
```  2938   apply (drule tan_total_pos)
```
```  2939   apply (cut_tac [2] y="-y" in tan_total_pos, safe)
```
```  2940   apply (rule_tac [3] x = "-x" in exI)
```
```  2941   apply (auto del: exI intro!: exI)
```
```  2942   done
```
```  2943
```
```  2944 lemma tan_total: "EX! x. -(pi/2) < x & x < (pi/2) & tan x = y"
```
```  2945   apply (cut_tac y = y in lemma_tan_total1, auto)
```
```  2946   apply (cut_tac x = xa and y = y in linorder_less_linear, auto)
```
```  2947   apply (subgoal_tac [2] "\<exists>z. y < z & z < xa & DERIV tan z :> 0")
```
```  2948   apply (subgoal_tac "\<exists>z. xa < z & z < y & DERIV tan z :> 0")
```
```  2949   apply (rule_tac [4] Rolle)
```
```  2950   apply (rule_tac [2] Rolle)
```
```  2951   apply (auto del: exI intro!: DERIV_tan DERIV_isCont exI
```
```  2952               simp add: real_differentiable_def)
```
```  2953   txt{*Now, simulate TRYALL*}
```
```  2954   apply (rule_tac [!] DERIV_tan asm_rl)
```
```  2955   apply (auto dest!: DERIV_unique [OF _ DERIV_tan]
```
```  2956               simp add: cos_gt_zero_pi [THEN less_imp_neq, THEN not_sym])
```
```  2957   done
```
```  2958
```
```  2959 lemma tan_monotone:
```
```  2960   assumes "- (pi / 2) < y" and "y < x" and "x < pi / 2"
```
```  2961   shows "tan y < tan x"
```
```  2962 proof -
```
```  2963   have "\<forall>x'. y \<le> x' \<and> x' \<le> x \<longrightarrow> DERIV tan x' :> inverse ((cos x')\<^sup>2)"
```
```  2964   proof (rule allI, rule impI)
```
```  2965     fix x' :: real
```
```  2966     assume "y \<le> x' \<and> x' \<le> x"
```
```  2967     hence "-(pi/2) < x'" and "x' < pi/2" using assms by auto
```
```  2968     from cos_gt_zero_pi[OF this]
```
```  2969     have "cos x' \<noteq> 0" by auto
```
```  2970     thus "DERIV tan x' :> inverse ((cos x')\<^sup>2)" by (rule DERIV_tan)
```
```  2971   qed
```
```  2972   from MVT2[OF `y < x` this]
```
```  2973   obtain z where "y < z" and "z < x"
```
```  2974     and tan_diff: "tan x - tan y = (x - y) * inverse ((cos z)\<^sup>2)" by auto
```
```  2975   hence "- (pi / 2) < z" and "z < pi / 2" using assms by auto
```
```  2976   hence "0 < cos z" using cos_gt_zero_pi by auto
```
```  2977   hence inv_pos: "0 < inverse ((cos z)\<^sup>2)" by auto
```
```  2978   have "0 < x - y" using `y < x` by auto
```
```  2979   from mult_pos_pos [OF this inv_pos]
```
```  2980   have "0 < tan x - tan y" unfolding tan_diff by auto
```
```  2981   thus ?thesis by auto
```
```  2982 qed
```
```  2983
```
```  2984 lemma tan_monotone':
```
```  2985   assumes "- (pi / 2) < y"
```
```  2986     and "y < pi / 2"
```
```  2987     and "- (pi / 2) < x"
```
```  2988     and "x < pi / 2"
```
```  2989   shows "(y < x) = (tan y < tan x)"
```
```  2990 proof
```
```  2991   assume "y < x"
```
```  2992   thus "tan y < tan x"
```
```  2993     using tan_monotone and `- (pi / 2) < y` and `x < pi / 2` by auto
```
```  2994 next
```
```  2995   assume "tan y < tan x"
```
```  2996   show "y < x"
```
```  2997   proof (rule ccontr)
```
```  2998     assume "\<not> y < x" hence "x \<le> y" by auto
```
```  2999     hence "tan x \<le> tan y"
```
```  3000     proof (cases "x = y")
```
```  3001       case True thus ?thesis by auto
```
```  3002     next
```
```  3003       case False hence "x < y" using `x \<le> y` by auto
```
```  3004       from tan_monotone[OF `- (pi/2) < x` this `y < pi / 2`] show ?thesis by auto
```
```  3005     qed
```
```  3006     thus False using `tan y < tan x` by auto
```
```  3007   qed
```
```  3008 qed
```
```  3009
```
```  3010 lemma tan_inverse: "1 / (tan y) = tan (pi / 2 - y)"
```
```  3011   unfolding tan_def sin_cos_eq[of y] cos_sin_eq[of y] by auto
```
```  3012
```
```  3013 lemma tan_periodic_pi[simp]: "tan (x + pi) = tan x"
```
```  3014   by (simp add: tan_def)
```
```  3015
```
```  3016 lemma tan_periodic_nat[simp]:
```
```  3017   fixes n :: nat
```
```  3018   shows "tan (x + real n * pi) = tan x"
```
```  3019 proof (induct n arbitrary: x)
```
```  3020   case 0
```
```  3021   then show ?case by simp
```
```  3022 next
```
```  3023   case (Suc n)
```
```  3024   have split_pi_off: "x + real (Suc n) * pi = (x + real n * pi) + pi"
```
```  3025     unfolding Suc_eq_plus1 real_of_nat_add real_of_one distrib_right by auto
```
```  3026   show ?case unfolding split_pi_off using Suc by auto
```
```  3027 qed
```
```  3028
```
```  3029 lemma tan_periodic_int[simp]: fixes i :: int shows "tan (x + real i * pi) = tan x"
```
```  3030 proof (cases "0 \<le> i")
```
```  3031   case True
```
```  3032   hence i_nat: "real i = real (nat i)" by auto
```
```  3033   show ?thesis unfolding i_nat by auto
```
```  3034 next
```
```  3035   case False
```
```  3036   hence i_nat: "real i = - real (nat (-i))" by auto
```
```  3037   have "tan x = tan (x + real i * pi - real i * pi)"
```
```  3038     by auto
```
```  3039   also have "\<dots> = tan (x + real i * pi)"
```
```  3040     unfolding i_nat mult_minus_left diff_minus_eq_add by (rule tan_periodic_nat)
```
```  3041   finally show ?thesis by auto
```
```  3042 qed
```
```  3043
```
```  3044 lemma tan_periodic_n[simp]: "tan (x + numeral n * pi) = tan x"
```
```  3045   using tan_periodic_int[of _ "numeral n" ] unfolding real_numeral .
```
```  3046
```
```  3047 subsection {* Inverse Trigonometric Functions *}
```
```  3048
```
```  3049 definition arcsin :: "real => real"
```
```  3050   where "arcsin y = (THE x. -(pi/2) \<le> x & x \<le> pi/2 & sin x = y)"
```
```  3051
```
```  3052 definition arccos :: "real => real"
```
```  3053   where "arccos y = (THE x. 0 \<le> x & x \<le> pi & cos x = y)"
```
```  3054
```
```  3055 definition arctan :: "real => real"
```
```  3056   where "arctan y = (THE x. -(pi/2) < x & x < pi/2 & tan x = y)"
```
```  3057
```
```  3058 lemma arcsin:
```
```  3059   "-1 \<le> y \<Longrightarrow> y \<le> 1 \<Longrightarrow>
```
```  3060     -(pi/2) \<le> arcsin y & arcsin y \<le> pi/2 & sin(arcsin y) = y"
```
```  3061   unfolding arcsin_def by (rule theI' [OF sin_total])
```
```  3062
```
```  3063 lemma arcsin_pi:
```
```  3064   "-1 \<le> y \<Longrightarrow> y \<le> 1 \<Longrightarrow> -(pi/2) \<le> arcsin y & arcsin y \<le> pi & sin(arcsin y) = y"
```
```  3065   apply (drule (1) arcsin)
```
```  3066   apply (force intro: order_trans)
```
```  3067   done
```
```  3068
```
```  3069 lemma sin_arcsin [simp]: "-1 \<le> y \<Longrightarrow> y \<le> 1 \<Longrightarrow> sin(arcsin y) = y"
```
```  3070   by (blast dest: arcsin)
```
```  3071
```
```  3072 lemma arcsin_bounded: "-1 \<le> y \<Longrightarrow> y \<le> 1 \<Longrightarrow> -(pi/2) \<le> arcsin y & arcsin y \<le> pi/2"
```
```  3073   by (blast dest: arcsin)
```
```  3074
```
```  3075 lemma arcsin_lbound: "-1 \<le> y \<Longrightarrow> y \<le> 1 \<Longrightarrow> -(pi/2) \<le> arcsin y"
```
```  3076   by (blast dest: arcsin)
```
```  3077
```
```  3078 lemma arcsin_ubound: "-1 \<le> y \<Longrightarrow> y \<le> 1 \<Longrightarrow> arcsin y \<le> pi/2"
```
```  3079   by (blast dest: arcsin)
```
```  3080
```
```  3081 lemma arcsin_lt_bounded:
```
```  3082      "[| -1 < y; y < 1 |] ==> -(pi/2) < arcsin y & arcsin y < pi/2"
```
```  3083   apply (frule order_less_imp_le)
```
```  3084   apply (frule_tac y = y in order_less_imp_le)
```
```  3085   apply (frule arcsin_bounded)
```
```  3086   apply (safe, simp)
```
```  3087   apply (drule_tac y = "arcsin y" in order_le_imp_less_or_eq)
```
```  3088   apply (drule_tac [2] y = "pi/2" in order_le_imp_less_or_eq, safe)
```
```  3089   apply (drule_tac [!] f = sin in arg_cong, auto)
```
```  3090   done
```
```  3091
```
```  3092 lemma arcsin_sin: "[|-(pi/2) \<le> x; x \<le> pi/2 |] ==> arcsin(sin x) = x"
```
```  3093   apply (unfold arcsin_def)
```
```  3094   apply (rule the1_equality)
```
```  3095   apply (rule sin_total, auto)
```
```  3096   done
```
```  3097
```
```  3098 lemma arccos:
```
```  3099      "[| -1 \<le> y; y \<le> 1 |]
```
```  3100       ==> 0 \<le> arccos y & arccos y \<le> pi & cos(arccos y) = y"
```
```  3101   unfolding arccos_def by (rule theI' [OF cos_total])
```
```  3102
```
```  3103 lemma cos_arccos [simp]: "[| -1 \<le> y; y \<le> 1 |] ==> cos(arccos y) = y"
```
```  3104   by (blast dest: arccos)
```
```  3105
```
```  3106 lemma arccos_bounded: "[| -1 \<le> y; y \<le> 1 |] ==> 0 \<le> arccos y & arccos y \<le> pi"
```
```  3107   by (blast dest: arccos)
```
```  3108
```
```  3109 lemma arccos_lbound: "[| -1 \<le> y; y \<le> 1 |] ==> 0 \<le> arccos y"
```
```  3110   by (blast dest: arccos)
```
```  3111
```
```  3112 lemma arccos_ubound: "[| -1 \<le> y; y \<le> 1 |] ==> arccos y \<le> pi"
```
```  3113   by (blast dest: arccos)
```
```  3114
```
```  3115 lemma arccos_lt_bounded:
```
```  3116      "[| -1 < y; y < 1 |]
```
```  3117       ==> 0 < arccos y & arccos y < pi"
```
```  3118   apply (frule order_less_imp_le)
```
```  3119   apply (frule_tac y = y in order_less_imp_le)
```
```  3120   apply (frule arccos_bounded, auto)
```
```  3121   apply (drule_tac y = "arccos y" in order_le_imp_less_or_eq)
```
```  3122   apply (drule_tac [2] y = pi in order_le_imp_less_or_eq, auto)
```
```  3123   apply (drule_tac [!] f = cos in arg_cong, auto)
```
```  3124   done
```
```  3125
```
```  3126 lemma arccos_cos: "[|0 \<le> x; x \<le> pi |] ==> arccos(cos x) = x"
```
```  3127   apply (simp add: arccos_def)
```
```  3128   apply (auto intro!: the1_equality cos_total)
```
```  3129   done
```
```  3130
```
```  3131 lemma arccos_cos2: "[|x \<le> 0; -pi \<le> x |] ==> arccos(cos x) = -x"
```
```  3132   apply (simp add: arccos_def)
```
```  3133   apply (auto intro!: the1_equality cos_total)
```
```  3134   done
```
```  3135
```
```  3136 lemma cos_arcsin: "\<lbrakk>-1 \<le> x; x \<le> 1\<rbrakk> \<Longrightarrow> cos (arcsin x) = sqrt (1 - x\<^sup>2)"
```
```  3137   apply (subgoal_tac "x\<^sup>2 \<le> 1")
```
```  3138   apply (rule power2_eq_imp_eq)
```
```  3139   apply (simp add: cos_squared_eq)
```
```  3140   apply (rule cos_ge_zero)
```
```  3141   apply (erule (1) arcsin_lbound)
```
```  3142   apply (erule (1) arcsin_ubound)
```
```  3143   apply simp
```
```  3144   apply (subgoal_tac "\<bar>x\<bar>\<^sup>2 \<le> 1\<^sup>2", simp)
```
```  3145   apply (rule power_mono, simp, simp)
```
```  3146   done
```
```  3147
```
```  3148 lemma sin_arccos: "\<lbrakk>-1 \<le> x; x \<le> 1\<rbrakk> \<Longrightarrow> sin (arccos x) = sqrt (1 - x\<^sup>2)"
```
```  3149   apply (subgoal_tac "x\<^sup>2 \<le> 1")
```
```  3150   apply (rule power2_eq_imp_eq)
```
```  3151   apply (simp add: sin_squared_eq)
```
```  3152   apply (rule sin_ge_zero)
```
```  3153   apply (erule (1) arccos_lbound)
```
```  3154   apply (erule (1) arccos_ubound)
```
```  3155   apply simp
```
```  3156   apply (subgoal_tac "\<bar>x\<bar>\<^sup>2 \<le> 1\<^sup>2", simp)
```
```  3157   apply (rule power_mono, simp, simp)
```
```  3158   done
```
```  3159
```
```  3160 lemma arctan [simp]: "- (pi/2) < arctan y  & arctan y < pi/2 & tan (arctan y) = y"
```
```  3161   unfolding arctan_def by (rule theI' [OF tan_total])
```
```  3162
```
```  3163 lemma tan_arctan: "tan (arctan y) = y"
```
```  3164   by auto
```
```  3165
```
```  3166 lemma arctan_bounded: "- (pi/2) < arctan y  & arctan y < pi/2"
```
```  3167   by (auto simp only: arctan)
```
```  3168
```
```  3169 lemma arctan_lbound: "- (pi/2) < arctan y"
```
```  3170   by auto
```
```  3171
```
```  3172 lemma arctan_ubound: "arctan y < pi/2"
```
```  3173   by (auto simp only: arctan)
```
```  3174
```
```  3175 lemma arctan_unique:
```
```  3176   assumes "-(pi/2) < x"
```
```  3177     and "x < pi/2"
```
```  3178     and "tan x = y"
```
```  3179   shows "arctan y = x"
```
```  3180   using assms arctan [of y] tan_total [of y] by (fast elim: ex1E)
```
```  3181
```
```  3182 lemma arctan_tan: "-(pi/2) < x \<Longrightarrow> x < pi/2 \<Longrightarrow> arctan (tan x) = x"
```
```  3183   by (rule arctan_unique) simp_all
```
```  3184
```
```  3185 lemma arctan_zero_zero [simp]: "arctan 0 = 0"
```
```  3186   by (rule arctan_unique) simp_all
```
```  3187
```
```  3188 lemma arctan_minus: "arctan (- x) = - arctan x"
```
```  3189   apply (rule arctan_unique)
```
```  3190   apply (simp only: neg_less_iff_less arctan_ubound)
```
```  3191   apply (metis minus_less_iff arctan_lbound)
```
```  3192   apply simp
```
```  3193   done
```
```  3194
```
```  3195 lemma cos_arctan_not_zero [simp]: "cos (arctan x) \<noteq> 0"
```
```  3196   by (intro less_imp_neq [symmetric] cos_gt_zero_pi
```
```  3197     arctan_lbound arctan_ubound)
```
```  3198
```
```  3199 lemma cos_arctan: "cos (arctan x) = 1 / sqrt (1 + x\<^sup>2)"
```
```  3200 proof (rule power2_eq_imp_eq)
```
```  3201   have "0 < 1 + x\<^sup>2" by (simp add: add_pos_nonneg)
```
```  3202   show "0 \<le> 1 / sqrt (1 + x\<^sup>2)" by simp
```
```  3203   show "0 \<le> cos (arctan x)"
```
```  3204     by (intro less_imp_le cos_gt_zero_pi arctan_lbound arctan_ubound)
```
```  3205   have "(cos (arctan x))\<^sup>2 * (1 + (tan (arctan x))\<^sup>2) = 1"
```
```  3206     unfolding tan_def by (simp add: distrib_left power_divide)
```
```  3207   thus "(cos (arctan x))\<^sup>2 = (1 / sqrt (1 + x\<^sup>2))\<^sup>2"
```
```  3208     using `0 < 1 + x\<^sup>2` by (simp add: power_divide eq_divide_eq)
```
```  3209 qed
```
```  3210
```
```  3211 lemma sin_arctan: "sin (arctan x) = x / sqrt (1 + x\<^sup>2)"
```
```  3212   using add_pos_nonneg [OF zero_less_one zero_le_power2 [of x]]
```
```  3213   using tan_arctan [of x] unfolding tan_def cos_arctan
```
```  3214   by (simp add: eq_divide_eq)
```
```  3215
```
```  3216 lemma tan_sec: "cos x \<noteq> 0 ==> 1 + (tan x)\<^sup>2 = (inverse (cos x))\<^sup>2"
```
```  3217   apply (rule power_inverse [THEN subst])
```
```  3218   apply (rule_tac c1 = "(cos x)\<^sup>2" in real_mult_right_cancel [THEN iffD1])
```
```  3219   apply (auto dest: field_power_not_zero
```
```  3220           simp add: power_mult_distrib distrib_right power_divide tan_def
```
```  3221                     mult_assoc power_inverse [symmetric])
```
```  3222   done
```
```  3223
```
```  3224 lemma arctan_less_iff: "arctan x < arctan y \<longleftrightarrow> x < y"
```
```  3225   by (metis tan_monotone' arctan_lbound arctan_ubound tan_arctan)
```
```  3226
```
```  3227 lemma arctan_le_iff: "arctan x \<le> arctan y \<longleftrightarrow> x \<le> y"
```
```  3228   by (simp only: not_less [symmetric] arctan_less_iff)
```
```  3229
```
```  3230 lemma arctan_eq_iff: "arctan x = arctan y \<longleftrightarrow> x = y"
```
```  3231   by (simp only: eq_iff [where 'a=real] arctan_le_iff)
```
```  3232
```
```  3233 lemma zero_less_arctan_iff [simp]: "0 < arctan x \<longleftrightarrow> 0 < x"
```
```  3234   using arctan_less_iff [of 0 x] by simp
```
```  3235
```
```  3236 lemma arctan_less_zero_iff [simp]: "arctan x < 0 \<longleftrightarrow> x < 0"
```
```  3237   using arctan_less_iff [of x 0] by simp
```
```  3238
```
```  3239 lemma zero_le_arctan_iff [simp]: "0 \<le> arctan x \<longleftrightarrow> 0 \<le> x"
```
```  3240   using arctan_le_iff [of 0 x] by simp
```
```  3241
```
```  3242 lemma arctan_le_zero_iff [simp]: "arctan x \<le> 0 \<longleftrightarrow> x \<le> 0"
```
```  3243   using arctan_le_iff [of x 0] by simp
```
```  3244
```
```  3245 lemma arctan_eq_zero_iff [simp]: "arctan x = 0 \<longleftrightarrow> x = 0"
```
```  3246   using arctan_eq_iff [of x 0] by simp
```
```  3247
```
```  3248 lemma continuous_on_arcsin': "continuous_on {-1 .. 1} arcsin"
```
```  3249 proof -
```
```  3250   have "continuous_on (sin ` {- pi / 2 .. pi / 2}) arcsin"
```
```  3251     by (rule continuous_on_inv) (auto intro: continuous_on_intros simp: arcsin_sin)
```
```  3252   also have "sin ` {- pi / 2 .. pi / 2} = {-1 .. 1}"
```
```  3253   proof safe
```
```  3254     fix x :: real
```
```  3255     assume "x \<in> {-1..1}"
```
```  3256     then show "x \<in> sin ` {- pi / 2..pi / 2}"
```
```  3257       using arcsin_lbound arcsin_ubound
```
```  3258       by (intro image_eqI[where x="arcsin x"]) auto
```
```  3259   qed simp
```
```  3260   finally show ?thesis .
```
```  3261 qed
```
```  3262
```
```  3263 lemma continuous_on_arcsin [continuous_on_intros]:
```
```  3264   "continuous_on s f \<Longrightarrow> (\<forall>x\<in>s. -1 \<le> f x \<and> f x \<le> 1) \<Longrightarrow> continuous_on s (\<lambda>x. arcsin (f x))"
```
```  3265   using continuous_on_compose[of s f, OF _ continuous_on_subset[OF  continuous_on_arcsin']]
```
```  3266   by (auto simp: comp_def subset_eq)
```
```  3267
```
```  3268 lemma isCont_arcsin: "-1 < x \<Longrightarrow> x < 1 \<Longrightarrow> isCont arcsin x"
```
```  3269   using continuous_on_arcsin'[THEN continuous_on_subset, of "{ -1 <..< 1 }"]
```
```  3270   by (auto simp: continuous_on_eq_continuous_at subset_eq)
```
```  3271
```
```  3272 lemma continuous_on_arccos': "continuous_on {-1 .. 1} arccos"
```
```  3273 proof -
```
```  3274   have "continuous_on (cos ` {0 .. pi}) arccos"
```
```  3275     by (rule continuous_on_inv) (auto intro: continuous_on_intros simp: arccos_cos)
```
```  3276   also have "cos ` {0 .. pi} = {-1 .. 1}"
```
```  3277   proof safe
```
```  3278     fix x :: real
```
```  3279     assume "x \<in> {-1..1}"
```
```  3280     then show "x \<in> cos ` {0..pi}"
```
```  3281       using arccos_lbound arccos_ubound
```
```  3282       by (intro image_eqI[where x="arccos x"]) auto
```
```  3283   qed simp
```
```  3284   finally show ?thesis .
```
```  3285 qed
```
```  3286
```
```  3287 lemma continuous_on_arccos [continuous_on_intros]:
```
```  3288   "continuous_on s f \<Longrightarrow> (\<forall>x\<in>s. -1 \<le> f x \<and> f x \<le> 1) \<Longrightarrow> continuous_on s (\<lambda>x. arccos (f x))"
```
```  3289   using continuous_on_compose[of s f, OF _ continuous_on_subset[OF  continuous_on_arccos']]
```
```  3290   by (auto simp: comp_def subset_eq)
```
```  3291
```
```  3292 lemma isCont_arccos: "-1 < x \<Longrightarrow> x < 1 \<Longrightarrow> isCont arccos x"
```
```  3293   using continuous_on_arccos'[THEN continuous_on_subset, of "{ -1 <..< 1 }"]
```
```  3294   by (auto simp: continuous_on_eq_continuous_at subset_eq)
```
```  3295
```
```  3296 lemma isCont_arctan: "isCont arctan x"
```
```  3297   apply (rule arctan_lbound [of x, THEN dense, THEN exE], clarify)
```
```  3298   apply (rule arctan_ubound [of x, THEN dense, THEN exE], clarify)
```
```  3299   apply (subgoal_tac "isCont arctan (tan (arctan x))", simp)
```
```  3300   apply (erule (1) isCont_inverse_function2 [where f=tan])
```
```  3301   apply (metis arctan_tan order_le_less_trans order_less_le_trans)
```
```  3302   apply (metis cos_gt_zero_pi isCont_tan order_less_le_trans less_le)
```
```  3303   done
```
```  3304
```
```  3305 lemma tendsto_arctan [tendsto_intros]: "(f ---> x) F \<Longrightarrow> ((\<lambda>x. arctan (f x)) ---> arctan x) F"
```
```  3306   by (rule isCont_tendsto_compose [OF isCont_arctan])
```
```  3307
```
```  3308 lemma continuous_arctan [continuous_intros]: "continuous F f \<Longrightarrow> continuous F (\<lambda>x. arctan (f x))"
```
```  3309   unfolding continuous_def by (rule tendsto_arctan)
```
```  3310
```
```  3311 lemma continuous_on_arctan [continuous_on_intros]: "continuous_on s f \<Longrightarrow> continuous_on s (\<lambda>x. arctan (f x))"
```
```  3312   unfolding continuous_on_def by (auto intro: tendsto_arctan)
```
```  3313
```
```  3314 lemma DERIV_arcsin:
```
```  3315   "\<lbrakk>-1 < x; x < 1\<rbrakk> \<Longrightarrow> DERIV arcsin x :> inverse (sqrt (1 - x\<^sup>2))"
```
```  3316   apply (rule DERIV_inverse_function [where f=sin and a="-1" and b="1"])
```
```  3317   apply (rule DERIV_cong [OF DERIV_sin])
```
```  3318   apply (simp add: cos_arcsin)
```
```  3319   apply (subgoal_tac "\<bar>x\<bar>\<^sup>2 < 1\<^sup>2", simp)
```
```  3320   apply (rule power_strict_mono, simp, simp, simp)
```
```  3321   apply assumption
```
```  3322   apply assumption
```
```  3323   apply simp
```
```  3324   apply (erule (1) isCont_arcsin)
```
```  3325   done
```
```  3326
```
```  3327 lemma DERIV_arccos:
```
```  3328   "\<lbrakk>-1 < x; x < 1\<rbrakk> \<Longrightarrow> DERIV arccos x :> inverse (- sqrt (1 - x\<^sup>2))"
```
```  3329   apply (rule DERIV_inverse_function [where f=cos and a="-1" and b="1"])
```
```  3330   apply (rule DERIV_cong [OF DERIV_cos])
```
```  3331   apply (simp add: sin_arccos)
```
```  3332   apply (subgoal_tac "\<bar>x\<bar>\<^sup>2 < 1\<^sup>2", simp)
```
```  3333   apply (rule power_strict_mono, simp, simp, simp)
```
```  3334   apply assumption
```
```  3335   apply assumption
```
```  3336   apply simp
```
```  3337   apply (erule (1) isCont_arccos)
```
```  3338   done
```
```  3339
```
```  3340 lemma DERIV_arctan: "DERIV arctan x :> inverse (1 + x\<^sup>2)"
```
```  3341   apply (rule DERIV_inverse_function [where f=tan and a="x - 1" and b="x + 1"])
```
```  3342   apply (rule DERIV_cong [OF DERIV_tan])
```
```  3343   apply (rule cos_arctan_not_zero)
```
```  3344   apply (simp add: power_inverse tan_sec [symmetric])
```
```  3345   apply (subgoal_tac "0 < 1 + x\<^sup>2", simp)
```
```  3346   apply (simp add: add_pos_nonneg)
```
```  3347   apply (simp, simp, simp, rule isCont_arctan)
```
```  3348   done
```
```  3349
```
```  3350 declare
```
```  3351   DERIV_arcsin[THEN DERIV_chain2, THEN DERIV_cong, DERIV_intros]
```
```  3352   DERIV_arccos[THEN DERIV_chain2, THEN DERIV_cong, DERIV_intros]
```
```  3353   DERIV_arctan[THEN DERIV_chain2, THEN DERIV_cong, DERIV_intros]
```
```  3354
```
```  3355 lemma filterlim_tan_at_right: "filterlim tan at_bot (at_right (- pi/2))"
```
```  3356   by (rule filterlim_at_bot_at_right[where Q="\<lambda>x. - pi/2 < x \<and> x < pi/2" and P="\<lambda>x. True" and g=arctan])
```
```  3357      (auto simp: le_less eventually_at dist_real_def simp del: less_divide_eq_numeral1
```
```  3358            intro!: tan_monotone exI[of _ "pi/2"])
```
```  3359
```
```  3360 lemma filterlim_tan_at_left: "filterlim tan at_top (at_left (pi/2))"
```
```  3361   by (rule filterlim_at_top_at_left[where Q="\<lambda>x. - pi/2 < x \<and> x < pi/2" and P="\<lambda>x. True" and g=arctan])
```
```  3362      (auto simp: le_less eventually_at dist_real_def simp del: less_divide_eq_numeral1
```
```  3363            intro!: tan_monotone exI[of _ "pi/2"])
```
```  3364
```
```  3365 lemma tendsto_arctan_at_top: "(arctan ---> (pi/2)) at_top"
```
```  3366 proof (rule tendstoI)
```
```  3367   fix e :: real
```
```  3368   assume "0 < e"
```
```  3369   def y \<equiv> "pi/2 - min (pi/2) e"
```
```  3370   then have y: "0 \<le> y" "y < pi/2" "pi/2 \<le> e + y"
```
```  3371     using `0 < e` by auto
```
```  3372
```
```  3373   show "eventually (\<lambda>x. dist (arctan x) (pi / 2) < e) at_top"
```
```  3374   proof (intro eventually_at_top_dense[THEN iffD2] exI allI impI)
```
```  3375     fix x
```
```  3376     assume "tan y < x"
```
```  3377     then have "arctan (tan y) < arctan x"
```
```  3378       by (simp add: arctan_less_iff)
```
```  3379     with y have "y < arctan x"
```
```  3380       by (subst (asm) arctan_tan) simp_all
```
```  3381     with arctan_ubound[of x, arith] y `0 < e`
```
```  3382     show "dist (arctan x) (pi / 2) < e"
```
```  3383       by (simp add: dist_real_def)
```
```  3384   qed
```
```  3385 qed
```
```  3386
```
```  3387 lemma tendsto_arctan_at_bot: "(arctan ---> - (pi/2)) at_bot"
```
```  3388   unfolding filterlim_at_bot_mirror arctan_minus
```
```  3389   by (intro tendsto_minus tendsto_arctan_at_top)
```
```  3390
```
```  3391
```
```  3392 subsection {* More Theorems about Sin and Cos *}
```
```  3393
```
```  3394 lemma cos_45: "cos (pi / 4) = sqrt 2 / 2"
```
```  3395 proof -
```
```  3396   let ?c = "cos (pi / 4)" and ?s = "sin (pi / 4)"
```
```  3397   have nonneg: "0 \<le> ?c"
```
```  3398     by (simp add: cos_ge_zero)
```
```  3399   have "0 = cos (pi / 4 + pi / 4)"
```
```  3400     by simp
```
```  3401   also have "cos (pi / 4 + pi / 4) = ?c\<^sup>2 - ?s\<^sup>2"
```
```  3402     by (simp only: cos_add power2_eq_square)
```
```  3403   also have "\<dots> = 2 * ?c\<^sup>2 - 1"
```
```  3404     by (simp add: sin_squared_eq)
```
```  3405   finally have "?c\<^sup>2 = (sqrt 2 / 2)\<^sup>2"
```
```  3406     by (simp add: power_divide)
```
```  3407   thus ?thesis
```
```  3408     using nonneg by (rule power2_eq_imp_eq) simp
```
```  3409 qed
```
```  3410
```
```  3411 lemma cos_30: "cos (pi / 6) = sqrt 3 / 2"
```
```  3412 proof -
```
```  3413   let ?c = "cos (pi / 6)" and ?s = "sin (pi / 6)"
```
```  3414   have pos_c: "0 < ?c"
```
```  3415     by (rule cos_gt_zero, simp, simp)
```
```  3416   have "0 = cos (pi / 6 + pi / 6 + pi / 6)"
```
```  3417     by simp
```
```  3418   also have "\<dots> = (?c * ?c - ?s * ?s) * ?c - (?s * ?c + ?c * ?s) * ?s"
```
```  3419     by (simp only: cos_add sin_add)
```
```  3420   also have "\<dots> = ?c * (?c\<^sup>2 - 3 * ?s\<^sup>2)"
```
```  3421     by (simp add: algebra_simps power2_eq_square)
```
```  3422   finally have "?c\<^sup>2 = (sqrt 3 / 2)\<^sup>2"
```
```  3423     using pos_c by (simp add: sin_squared_eq power_divide)
```
```  3424   thus ?thesis
```
```  3425     using pos_c [THEN order_less_imp_le]
```
```  3426     by (rule power2_eq_imp_eq) simp
```
```  3427 qed
```
```  3428
```
```  3429 lemma sin_45: "sin (pi / 4) = sqrt 2 / 2"
```
```  3430   by (simp add: sin_cos_eq cos_45)
```
```  3431
```
```  3432 lemma sin_60: "sin (pi / 3) = sqrt 3 / 2"
```
```  3433   by (simp add: sin_cos_eq cos_30)
```
```  3434
```
```  3435 lemma cos_60: "cos (pi / 3) = 1 / 2"
```
```  3436   apply (rule power2_eq_imp_eq)
```
```  3437   apply (simp add: cos_squared_eq sin_60 power_divide)
```
```  3438   apply (rule cos_ge_zero, rule order_trans [where y=0], simp_all)
```
```  3439   done
```
```  3440
```
```  3441 lemma sin_30: "sin (pi / 6) = 1 / 2"
```
```  3442   by (simp add: sin_cos_eq cos_60)
```
```  3443
```
```  3444 lemma tan_30: "tan (pi / 6) = 1 / sqrt 3"
```
```  3445   unfolding tan_def by (simp add: sin_30 cos_30)
```
```  3446
```
```  3447 lemma tan_45: "tan (pi / 4) = 1"
```
```  3448   unfolding tan_def by (simp add: sin_45 cos_45)
```
```  3449
```
```  3450 lemma tan_60: "tan (pi / 3) = sqrt 3"
```
```  3451   unfolding tan_def by (simp add: sin_60 cos_60)
```
```  3452
```
```  3453 lemma sin_cos_npi [simp]: "sin (real (Suc (2 * n)) * pi / 2) = (-1) ^ n"
```
```  3454 proof -
```
```  3455   have "sin ((real n + 1/2) * pi) = cos (real n * pi)"
```
```  3456     by (auto simp add: algebra_simps sin_add)
```
```  3457   thus ?thesis
```
```  3458     by (simp add: real_of_nat_Suc distrib_right add_divide_distrib
```
```  3459                   mult_commute [of pi])
```
```  3460 qed
```
```  3461
```
```  3462 lemma cos_2npi [simp]: "cos (2 * real (n::nat) * pi) = 1"
```
```  3463   by (simp add: cos_double mult_assoc power_add [symmetric] numeral_2_eq_2)
```
```  3464
```
```  3465 lemma cos_3over2_pi [simp]: "cos (3 / 2 * pi) = 0"
```
```  3466   apply (subgoal_tac "cos (pi + pi/2) = 0", simp)
```
```  3467   apply (subst cos_add, simp)
```
```  3468   done
```
```  3469
```
```  3470 lemma sin_2npi [simp]: "sin (2 * real (n::nat) * pi) = 0"
```
```  3471   by (auto simp add: mult_assoc)
```
```  3472
```
```  3473 lemma sin_3over2_pi [simp]: "sin (3 / 2 * pi) = - 1"
```
```  3474   apply (subgoal_tac "sin (pi + pi/2) = - 1", simp)
```
```  3475   apply (subst sin_add, simp)
```
```  3476   done
```
```  3477
```
```  3478 lemma cos_pi_eq_zero [simp]: "cos (pi * real (Suc (2 * m)) / 2) = 0"
```
```  3479   apply (simp only: cos_add sin_add real_of_nat_Suc distrib_right distrib_left add_divide_distrib)
```
```  3480   apply auto
```
```  3481   done
```
```  3482
```
```  3483 lemma DERIV_cos_add [simp]: "DERIV (\<lambda>x. cos (x + k)) xa :> - sin (xa + k)"
```
```  3484   by (auto intro!: DERIV_intros)
```
```  3485
```
```  3486 lemma sin_zero_abs_cos_one: "sin x = 0 ==> \<bar>cos x\<bar> = 1"
```
```  3487   by (auto simp add: sin_zero_iff even_mult_two_ex)
```
```  3488
```
```  3489 lemma cos_one_sin_zero: "cos x = 1 ==> sin x = 0"
```
```  3490   using sin_cos_squared_add3 [where x = x] by auto
```
```  3491
```
```  3492
```
```  3493 subsection {* Machins formula *}
```
```  3494
```
```  3495 lemma arctan_one: "arctan 1 = pi / 4"
```
```  3496   by (rule arctan_unique, simp_all add: tan_45 m2pi_less_pi)
```
```  3497
```
```  3498 lemma tan_total_pi4:
```
```  3499   assumes "\<bar>x\<bar> < 1"
```
```  3500   shows "\<exists>z. - (pi / 4) < z \<and> z < pi / 4 \<and> tan z = x"
```
```  3501 proof
```
```  3502   show "- (pi / 4) < arctan x \<and> arctan x < pi / 4 \<and> tan (arctan x) = x"
```
```  3503     unfolding arctan_one [symmetric] arctan_minus [symmetric]
```
```  3504     unfolding arctan_less_iff using assms by auto
```
```  3505 qed
```
```  3506
```
```  3507 lemma arctan_add:
```
```  3508   assumes "\<bar>x\<bar> \<le> 1" and "\<bar>y\<bar> < 1"
```
```  3509   shows "arctan x + arctan y = arctan ((x + y) / (1 - x * y))"
```
```  3510 proof (rule arctan_unique [symmetric])
```
```  3511   have "- (pi / 4) \<le> arctan x" and "- (pi / 4) < arctan y"
```
```  3512     unfolding arctan_one [symmetric] arctan_minus [symmetric]
```
```  3513     unfolding arctan_le_iff arctan_less_iff using assms by auto
```
```  3514   from add_le_less_mono [OF this]
```
```  3515   show 1: "- (pi / 2) < arctan x + arctan y" by simp
```
```  3516   have "arctan x \<le> pi / 4" and "arctan y < pi / 4"
```
```  3517     unfolding arctan_one [symmetric]
```
```  3518     unfolding arctan_le_iff arctan_less_iff using assms by auto
```
```  3519   from add_le_less_mono [OF this]
```
```  3520   show 2: "arctan x + arctan y < pi / 2" by simp
```
```  3521   show "tan (arctan x + arctan y) = (x + y) / (1 - x * y)"
```
```  3522     using cos_gt_zero_pi [OF 1 2] by (simp add: tan_add)
```
```  3523 qed
```
```  3524
```
```  3525 theorem machin: "pi / 4 = 4 * arctan (1/5) - arctan (1 / 239)"
```
```  3526 proof -
```
```  3527   have "\<bar>1 / 5\<bar> < (1 :: real)" by auto
```
```  3528   from arctan_add[OF less_imp_le[OF this] this]
```
```  3529   have "2 * arctan (1 / 5) = arctan (5 / 12)" by auto
```
```  3530   moreover
```
```  3531   have "\<bar>5 / 12\<bar> < (1 :: real)" by auto
```
```  3532   from arctan_add[OF less_imp_le[OF this] this]
```
```  3533   have "2 * arctan (5 / 12) = arctan (120 / 119)" by auto
```
```  3534   moreover
```
```  3535   have "\<bar>1\<bar> \<le> (1::real)" and "\<bar>1 / 239\<bar> < (1::real)" by auto
```
```  3536   from arctan_add[OF this]
```
```  3537   have "arctan 1 + arctan (1 / 239) = arctan (120 / 119)" by auto
```
```  3538   ultimately have "arctan 1 + arctan (1 / 239) = 4 * arctan (1 / 5)" by auto
```
```  3539   thus ?thesis unfolding arctan_one by algebra
```
```  3540 qed
```
```  3541
```
```  3542
```
```  3543 subsection {* Introducing the arcus tangens power series *}
```
```  3544
```
```  3545 lemma monoseq_arctan_series:
```
```  3546   fixes x :: real
```
```  3547   assumes "\<bar>x\<bar> \<le> 1"
```
```  3548   shows "monoseq (\<lambda> n. 1 / real (n*2+1) * x^(n*2+1))" (is "monoseq ?a")
```
```  3549 proof (cases "x = 0")
```
```  3550   case True
```
```  3551   thus ?thesis unfolding monoseq_def One_nat_def by auto
```
```  3552 next
```
```  3553   case False
```
```  3554   have "norm x \<le> 1" and "x \<le> 1" and "-1 \<le> x" using assms by auto
```
```  3555   show "monoseq ?a"
```
```  3556   proof -
```
```  3557     {
```
```  3558       fix n
```
```  3559       fix x :: real
```
```  3560       assume "0 \<le> x" and "x \<le> 1"
```
```  3561       have "1 / real (Suc (Suc n * 2)) * x ^ Suc (Suc n * 2) \<le>
```
```  3562         1 / real (Suc (n * 2)) * x ^ Suc (n * 2)"
```
```  3563       proof (rule mult_mono)
```
```  3564         show "1 / real (Suc (Suc n * 2)) \<le> 1 / real (Suc (n * 2))"
```
```  3565           by (rule frac_le) simp_all
```
```  3566         show "0 \<le> 1 / real (Suc (n * 2))"
```
```  3567           by auto
```
```  3568         show "x ^ Suc (Suc n * 2) \<le> x ^ Suc (n * 2)"
```
```  3569           by (rule power_decreasing) (simp_all add: `0 \<le> x` `x \<le> 1`)
```
```  3570         show "0 \<le> x ^ Suc (Suc n * 2)"
```
```  3571           by (rule zero_le_power) (simp add: `0 \<le> x`)
```
```  3572       qed
```
```  3573     } note mono = this
```
```  3574
```
```  3575     show ?thesis
```
```  3576     proof (cases "0 \<le> x")
```
```  3577       case True from mono[OF this `x \<le> 1`, THEN allI]
```
```  3578       show ?thesis unfolding Suc_eq_plus1[symmetric]
```
```  3579         by (rule mono_SucI2)
```
```  3580     next
```
```  3581       case False
```
```  3582       hence "0 \<le> -x" and "-x \<le> 1" using `-1 \<le> x` by auto
```
```  3583       from mono[OF this]
```
```  3584       have "\<And>n. 1 / real (Suc (Suc n * 2)) * x ^ Suc (Suc n * 2) \<ge>
```
```  3585         1 / real (Suc (n * 2)) * x ^ Suc (n * 2)" using `0 \<le> -x` by auto
```
```  3586       thus ?thesis unfolding Suc_eq_plus1[symmetric] by (rule mono_SucI1[OF allI])
```
```  3587     qed
```
```  3588   qed
```
```  3589 qed
```
```  3590
```
```  3591 lemma zeroseq_arctan_series:
```
```  3592   fixes x :: real
```
```  3593   assumes "\<bar>x\<bar> \<le> 1"
```
```  3594   shows "(\<lambda> n. 1 / real (n*2+1) * x^(n*2+1)) ----> 0" (is "?a ----> 0")
```
```  3595 proof (cases "x = 0")
```
```  3596   case True
```
```  3597   thus ?thesis
```
```  3598     unfolding One_nat_def by (auto simp add: tendsto_const)
```
```  3599 next
```
```  3600   case False
```
```  3601   have "norm x \<le> 1" and "x \<le> 1" and "-1 \<le> x" using assms by auto
```
```  3602   show "?a ----> 0"
```
```  3603   proof (cases "\<bar>x\<bar> < 1")
```
```  3604     case True
```
```  3605     hence "norm x < 1" by auto
```
```  3606     from tendsto_mult[OF LIMSEQ_inverse_real_of_nat LIMSEQ_power_zero[OF `norm x < 1`, THEN LIMSEQ_Suc]]
```
```  3607     have "(\<lambda>n. 1 / real (n + 1) * x ^ (n + 1)) ----> 0"
```
```  3608       unfolding inverse_eq_divide Suc_eq_plus1 by simp
```
```  3609     then show ?thesis using pos2 by (rule LIMSEQ_linear)
```
```  3610   next
```
```  3611     case False
```
```  3612     hence "x = -1 \<or> x = 1" using `\<bar>x\<bar> \<le> 1` by auto
```
```  3613     hence n_eq: "\<And> n. x ^ (n * 2 + 1) = x"
```
```  3614       unfolding One_nat_def by auto
```
```  3615     from tendsto_mult[OF LIMSEQ_inverse_real_of_nat[THEN LIMSEQ_linear, OF pos2, unfolded inverse_eq_divide] tendsto_const[of x]]
```
```  3616     show ?thesis unfolding n_eq Suc_eq_plus1 by auto
```
```  3617   qed
```
```  3618 qed
```
```  3619
```
```  3620 lemma summable_arctan_series:
```
```  3621   fixes x :: real and n :: nat
```
```  3622   assumes "\<bar>x\<bar> \<le> 1"
```
```  3623   shows "summable (\<lambda> k. (-1)^k * (1 / real (k*2+1) * x ^ (k*2+1)))"
```
```  3624   (is "summable (?c x)")
```
```  3625   by (rule summable_Leibniz(1), rule zeroseq_arctan_series[OF assms], rule monoseq_arctan_series[OF assms])
```
```  3626
```
```  3627 lemma less_one_imp_sqr_less_one:
```
```  3628   fixes x :: real
```
```  3629   assumes "\<bar>x\<bar> < 1"
```
```  3630   shows "x\<^sup>2 < 1"
```
```  3631 proof -
```
```  3632   have "\<bar>x\<^sup>2\<bar> < 1"
```
```  3633     by (metis abs_power2 assms pos2 power2_abs power_0 power_strict_decreasing zero_eq_power2 zero_less_abs_iff)
```
```  3634   thus ?thesis using zero_le_power2 by auto
```
```  3635 qed
```
```  3636
```
```  3637 lemma DERIV_arctan_series:
```
```  3638   assumes "\<bar> x \<bar> < 1"
```
```  3639   shows "DERIV (\<lambda> x'. \<Sum> k. (-1)^k * (1 / real (k*2+1) * x' ^ (k*2+1))) x :> (\<Sum> k. (-1)^k * x^(k*2))"
```
```  3640   (is "DERIV ?arctan _ :> ?Int")
```
```  3641 proof -
```
```  3642   let ?f = "\<lambda>n. if even n then (-1)^(n div 2) * 1 / real (Suc n) else 0"
```
```  3643
```
```  3644   have n_even: "\<And>n :: nat. even n \<Longrightarrow> 2 * (n div 2) = n"
```
```  3645     by presburger
```
```  3646   then have if_eq: "\<And>n x'. ?f n * real (Suc n) * x'^n =
```
```  3647     (if even n then (-1)^(n div 2) * x'^(2 * (n div 2)) else 0)"
```
```  3648     by auto
```
```  3649
```
```  3650   {
```
```  3651     fix x :: real
```
```  3652     assume "\<bar>x\<bar> < 1"
```
```  3653     hence "x\<^sup>2 < 1" by (rule less_one_imp_sqr_less_one)
```
```  3654     have "summable (\<lambda> n. -1 ^ n * (x\<^sup>2) ^n)"
```
```  3655       by (rule summable_Leibniz(1), auto intro!: LIMSEQ_realpow_zero monoseq_realpow `x\<^sup>2 < 1` order_less_imp_le[OF `x\<^sup>2 < 1`])
```
```  3656     hence "summable (\<lambda> n. -1 ^ n * x^(2*n))" unfolding power_mult .
```
```  3657   } note summable_Integral = this
```
```  3658
```
```  3659   {
```
```  3660     fix f :: "nat \<Rightarrow> real"
```
```  3661     have "\<And>x. f sums x = (\<lambda> n. if even n then f (n div 2) else 0) sums x"
```
```  3662     proof
```
```  3663       fix x :: real
```
```  3664       assume "f sums x"
```
```  3665       from sums_if[OF sums_zero this]
```
```  3666       show "(\<lambda>n. if even n then f (n div 2) else 0) sums x"
```
```  3667         by auto
```
```  3668     next
```
```  3669       fix x :: real
```
```  3670       assume "(\<lambda> n. if even n then f (n div 2) else 0) sums x"
```
```  3671       from LIMSEQ_linear[OF this[unfolded sums_def] pos2, unfolded sum_split_even_odd[unfolded mult_commute]]
```
```  3672       show "f sums x" unfolding sums_def by auto
```
```  3673     qed
```
```  3674     hence "op sums f = op sums (\<lambda> n. if even n then f (n div 2) else 0)" ..
```
```  3675   } note sums_even = this
```
```  3676
```
```  3677   have Int_eq: "(\<Sum>n. ?f n * real (Suc n) * x^n) = ?Int"
```
```  3678     unfolding if_eq mult_commute[of _ 2] suminf_def sums_even[of "\<lambda> n. -1 ^ n * x ^ (2 * n)", symmetric]
```
```  3679     by auto
```
```  3680
```
```  3681   {
```
```  3682     fix x :: real
```
```  3683     have if_eq': "\<And>n. (if even n then -1 ^ (n div 2) * 1 / real (Suc n) else 0) * x ^ Suc n =
```
```  3684       (if even n then -1 ^ (n div 2) * (1 / real (Suc (2 * (n div 2))) * x ^ Suc (2 * (n div 2))) else 0)"
```
```  3685       using n_even by auto
```
```  3686     have idx_eq: "\<And>n. n * 2 + 1 = Suc (2 * n)" by auto
```
```  3687     have "(\<Sum>n. ?f n * x^(Suc n)) = ?arctan x"
```
```  3688       unfolding if_eq' idx_eq suminf_def sums_even[of "\<lambda> n. -1 ^ n * (1 / real (Suc (2 * n)) * x ^ Suc (2 * n))", symmetric]
```
```  3689       by auto
```
```  3690   } note arctan_eq = this
```
```  3691
```
```  3692   have "DERIV (\<lambda> x. \<Sum> n. ?f n * x^(Suc n)) x :> (\<Sum> n. ?f n * real (Suc n) * x^n)"
```
```  3693   proof (rule DERIV_power_series')
```
```  3694     show "x \<in> {- 1 <..< 1}" using `\<bar> x \<bar> < 1` by auto
```
```  3695     {
```
```  3696       fix x' :: real
```
```  3697       assume x'_bounds: "x' \<in> {- 1 <..< 1}"
```
```  3698       hence "\<bar>x'\<bar> < 1" by auto
```
```  3699
```
```  3700       let ?S = "\<Sum> n. (-1)^n * x'^(2 * n)"
```
```  3701       show "summable (\<lambda> n. ?f n * real (Suc n) * x'^n)" unfolding if_eq
```
```  3702         by (rule sums_summable[where l="0 + ?S"], rule sums_if, rule sums_zero, rule summable_sums, rule summable_Integral[OF `\<bar>x'\<bar> < 1`])
```
```  3703     }
```
```  3704   qed auto
```
```  3705   thus ?thesis unfolding Int_eq arctan_eq .
```
```  3706 qed
```
```  3707
```
```  3708 lemma arctan_series:
```
```  3709   assumes "\<bar> x \<bar> \<le> 1"
```
```  3710   shows "arctan x = (\<Sum>k. (-1)^k * (1 / real (k*2+1) * x ^ (k*2+1)))"
```
```  3711   (is "_ = suminf (\<lambda> n. ?c x n)")
```
```  3712 proof -
```
```  3713   let ?c' = "\<lambda>x n. (-1)^n * x^(n*2)"
```
```  3714
```
```  3715   {
```
```  3716     fix r x :: real
```
```  3717     assume "0 < r" and "r < 1" and "\<bar> x \<bar> < r"
```
```  3718     have "\<bar>x\<bar> < 1" using `r < 1` and `\<bar>x\<bar> < r` by auto
```
```  3719     from DERIV_arctan_series[OF this] have "DERIV (\<lambda> x. suminf (?c x)) x :> (suminf (?c' x))" .
```
```  3720   } note DERIV_arctan_suminf = this
```
```  3721
```
```  3722   {
```
```  3723     fix x :: real
```
```  3724     assume "\<bar>x\<bar> \<le> 1"
```
```  3725     note summable_Leibniz[OF zeroseq_arctan_series[OF this] monoseq_arctan_series[OF this]]
```
```  3726   } note arctan_series_borders = this
```
```  3727
```
```  3728   {
```
```  3729     fix x :: real
```
```  3730     assume "\<bar>x\<bar> < 1"
```
```  3731     have "arctan x = (\<Sum>k. ?c x k)"
```
```  3732     proof -
```
```  3733       obtain r where "\<bar>x\<bar> < r" and "r < 1"
```
```  3734         using dense[OF `\<bar>x\<bar> < 1`] by blast
```
```  3735       hence "0 < r" and "-r < x" and "x < r" by auto
```
```  3736
```
```  3737       have suminf_eq_arctan_bounded: "\<And>x a b. \<lbrakk> -r < a ; b < r ; a < b ; a \<le> x ; x \<le> b \<rbrakk> \<Longrightarrow>
```
```  3738         suminf (?c x) - arctan x = suminf (?c a) - arctan a"
```
```  3739       proof -
```
```  3740         fix x a b
```
```  3741         assume "-r < a" and "b < r" and "a < b" and "a \<le> x" and "x \<le> b"
```
```  3742         hence "\<bar>x\<bar> < r" by auto
```
```  3743         show "suminf (?c x) - arctan x = suminf (?c a) - arctan a"
```
```  3744         proof (rule DERIV_isconst2[of "a" "b"])
```
```  3745           show "a < b" and "a \<le> x" and "x \<le> b"
```
```  3746             using `a < b` `a \<le> x` `x \<le> b` by auto
```
```  3747           have "\<forall>x. -r < x \<and> x < r \<longrightarrow> DERIV (\<lambda> x. suminf (?c x) - arctan x) x :> 0"
```
```  3748           proof (rule allI, rule impI)
```
```  3749             fix x
```
```  3750             assume "-r < x \<and> x < r"
```
```  3751             hence "\<bar>x\<bar> < r" by auto
```
```  3752             hence "\<bar>x\<bar> < 1" using `r < 1` by auto
```
```  3753             have "\<bar> - (x\<^sup>2) \<bar> < 1"
```
```  3754               using less_one_imp_sqr_less_one[OF `\<bar>x\<bar> < 1`] by auto
```
```  3755             hence "(\<lambda> n. (- (x\<^sup>2)) ^ n) sums (1 / (1 - (- (x\<^sup>2))))"
```
```  3756               unfolding real_norm_def[symmetric] by (rule geometric_sums)
```
```  3757             hence "(?c' x) sums (1 / (1 - (- (x\<^sup>2))))"
```
```  3758               unfolding power_mult_distrib[symmetric] power_mult nat_mult_commute[of _ 2] by auto
```
```  3759             hence suminf_c'_eq_geom: "inverse (1 + x\<^sup>2) = suminf (?c' x)"
```
```  3760               using sums_unique unfolding inverse_eq_divide by auto
```
```  3761             have "DERIV (\<lambda> x. suminf (?c x)) x :> (inverse (1 + x\<^sup>2))"
```
```  3762               unfolding suminf_c'_eq_geom
```
```  3763               by (rule DERIV_arctan_suminf[OF `0 < r` `r < 1` `\<bar>x\<bar> < r`])
```
```  3764             from DERIV_add_minus[OF this DERIV_arctan]
```
```  3765             show "DERIV (\<lambda> x. suminf (?c x) - arctan x) x :> 0"
```
```  3766               by auto
```
```  3767           qed
```
```  3768           hence DERIV_in_rball: "\<forall> y. a \<le> y \<and> y \<le> b \<longrightarrow> DERIV (\<lambda> x. suminf (?c x) - arctan x) y :> 0"
```
```  3769             using `-r < a` `b < r` by auto
```
```  3770           thus "\<forall> y. a < y \<and> y < b \<longrightarrow> DERIV (\<lambda> x. suminf (?c x) - arctan x) y :> 0"
```
```  3771             using `\<bar>x\<bar> < r` by auto
```
```  3772           show "\<forall> y. a \<le> y \<and> y \<le> b \<longrightarrow> isCont (\<lambda> x. suminf (?c x) - arctan x) y"
```
```  3773             using DERIV_in_rball DERIV_isCont by auto
```
```  3774         qed
```
```  3775       qed
```
```  3776
```
```  3777       have suminf_arctan_zero: "suminf (?c 0) - arctan 0 = 0"
```
```  3778         unfolding Suc_eq_plus1[symmetric] power_Suc2 mult_zero_right arctan_zero_zero suminf_zero
```
```  3779         by auto
```
```  3780
```
```  3781       have "suminf (?c x) - arctan x = 0"
```
```  3782       proof (cases "x = 0")
```
```  3783         case True
```
```  3784         thus ?thesis using suminf_arctan_zero by auto
```
```  3785       next
```
```  3786         case False
```
```  3787         hence "0 < \<bar>x\<bar>" and "- \<bar>x\<bar> < \<bar>x\<bar>" by auto
```
```  3788         have "suminf (?c (-\<bar>x\<bar>)) - arctan (-\<bar>x\<bar>) = suminf (?c 0) - arctan 0"
```
```  3789           by (rule suminf_eq_arctan_bounded[where x="0" and a="-\<bar>x\<bar>" and b="\<bar>x\<bar>", symmetric])
```
```  3790             (simp_all only: `\<bar>x\<bar> < r` `-\<bar>x\<bar> < \<bar>x\<bar>` neg_less_iff_less)
```
```  3791         moreover
```
```  3792         have "suminf (?c x) - arctan x = suminf (?c (-\<bar>x\<bar>)) - arctan (-\<bar>x\<bar>)"
```
```  3793           by (rule suminf_eq_arctan_bounded[where x="x" and a="-\<bar>x\<bar>" and b="\<bar>x\<bar>"])
```
```  3794              (simp_all only: `\<bar>x\<bar> < r` `-\<bar>x\<bar> < \<bar>x\<bar>` neg_less_iff_less)
```
```  3795         ultimately
```
```  3796         show ?thesis using suminf_arctan_zero by auto
```
```  3797       qed
```
```  3798       thus ?thesis by auto
```
```  3799     qed
```
```  3800   } note when_less_one = this
```
```  3801
```
```  3802   show "arctan x = suminf (\<lambda> n. ?c x n)"
```
```  3803   proof (cases "\<bar>x\<bar> < 1")
```
```  3804     case True
```
```  3805     thus ?thesis by (rule when_less_one)
```
```  3806   next
```
```  3807     case False
```
```  3808     hence "\<bar>x\<bar> = 1" using `\<bar>x\<bar> \<le> 1` by auto
```
```  3809     let ?a = "\<lambda>x n. \<bar>1 / real (n*2+1) * x^(n*2+1)\<bar>"
```
```  3810     let ?diff = "\<lambda> x n. \<bar> arctan x - (\<Sum> i = 0..<n. ?c x i)\<bar>"
```
```  3811     {
```
```  3812       fix n :: nat
```
```  3813       have "0 < (1 :: real)" by auto
```
```  3814       moreover
```
```  3815       {
```
```  3816         fix x :: real
```
```  3817         assume "0 < x" and "x < 1"
```
```  3818         hence "\<bar>x\<bar> \<le> 1" and "\<bar>x\<bar> < 1" by auto
```
```  3819         from `0 < x` have "0 < 1 / real (0 * 2 + (1::nat)) * x ^ (0 * 2 + 1)"
```
```  3820           by auto
```
```  3821         note bounds = mp[OF arctan_series_borders(2)[OF `\<bar>x\<bar> \<le> 1`] this, unfolded when_less_one[OF `\<bar>x\<bar> < 1`, symmetric], THEN spec]
```
```  3822         have "0 < 1 / real (n*2+1) * x^(n*2+1)"
```
```  3823           by (rule mult_pos_pos, auto simp only: zero_less_power[OF `0 < x`], auto)
```
```  3824         hence a_pos: "?a x n = 1 / real (n*2+1) * x^(n*2+1)"
```
```  3825           by (rule abs_of_pos)
```
```  3826         have "?diff x n \<le> ?a x n"
```
```  3827         proof (cases "even n")
```
```  3828           case True
```
```  3829           hence sgn_pos: "(-1)^n = (1::real)" by auto
```
```  3830           from `even n` obtain m where "2 * m = n"
```
```  3831             unfolding even_mult_two_ex by auto
```
```  3832           from bounds[of m, unfolded this atLeastAtMost_iff]
```
```  3833           have "\<bar>arctan x - (\<Sum>i = 0..<n. (?c x i))\<bar> \<le> (\<Sum>i = 0..<n + 1. (?c x i)) - (\<Sum>i = 0..<n. (?c x i))"
```
```  3834             by auto
```
```  3835           also have "\<dots> = ?c x n" unfolding One_nat_def by auto
```
```  3836           also have "\<dots> = ?a x n" unfolding sgn_pos a_pos by auto
```
```  3837           finally show ?thesis .
```
```  3838         next
```
```  3839           case False
```
```  3840           hence sgn_neg: "(-1)^n = (-1::real)" by auto
```
```  3841           from `odd n` obtain m where m_def: "2 * m + 1 = n"
```
```  3842             unfolding odd_Suc_mult_two_ex by auto
```
```  3843           hence m_plus: "2 * (m + 1) = n + 1" by auto
```
```  3844           from bounds[of "m + 1", unfolded this atLeastAtMost_iff, THEN conjunct1] bounds[of m, unfolded m_def atLeastAtMost_iff, THEN conjunct2]
```
```  3845           have "\<bar>arctan x - (\<Sum>i = 0..<n. (?c x i))\<bar> \<le> (\<Sum>i = 0..<n. (?c x i)) - (\<Sum>i = 0..<n+1. (?c x i))"
```
```  3846             by auto
```
```  3847           also have "\<dots> = - ?c x n" unfolding One_nat_def by auto
```
```  3848           also have "\<dots> = ?a x n" unfolding sgn_neg a_pos by auto
```
```  3849           finally show ?thesis .
```
```  3850         qed
```
```  3851         hence "0 \<le> ?a x n - ?diff x n" by auto
```
```  3852       }
```
```  3853       hence "\<forall> x \<in> { 0 <..< 1 }. 0 \<le> ?a x n - ?diff x n" by auto
```
```  3854       moreover have "\<And>x. isCont (\<lambda> x. ?a x n - ?diff x n) x"
```
```  3855         unfolding diff_conv_add_uminus divide_inverse
```
```  3856         by (auto intro!: isCont_add isCont_rabs isCont_ident isCont_minus isCont_arctan
```
```  3857           isCont_inverse isCont_mult isCont_power isCont_const isCont_setsum
```
```  3858           simp del: add_uminus_conv_diff)
```
```  3859       ultimately have "0 \<le> ?a 1 n - ?diff 1 n"
```
```  3860         by (rule LIM_less_bound)
```
```  3861       hence "?diff 1 n \<le> ?a 1 n" by auto
```
```  3862     }
```
```  3863     have "?a 1 ----> 0"
```
```  3864       unfolding tendsto_rabs_zero_iff power_one divide_inverse One_nat_def
```
```  3865       by (auto intro!: tendsto_mult LIMSEQ_linear LIMSEQ_inverse_real_of_nat)
```
```  3866     have "?diff 1 ----> 0"
```
```  3867     proof (rule LIMSEQ_I)
```
```  3868       fix r :: real
```
```  3869       assume "0 < r"
```
```  3870       obtain N :: nat where N_I: "\<And>n. N \<le> n \<Longrightarrow> ?a 1 n < r"
```
```  3871         using LIMSEQ_D[OF `?a 1 ----> 0` `0 < r`] by auto
```
```  3872       {
```
```  3873         fix n
```
```  3874         assume "N \<le> n" from `?diff 1 n \<le> ?a 1 n` N_I[OF this]
```
```  3875         have "norm (?diff 1 n - 0) < r" by auto
```
```  3876       }
```
```  3877       thus "\<exists> N. \<forall> n \<ge> N. norm (?diff 1 n - 0) < r" by blast
```
```  3878     qed
```
```  3879     from this [unfolded tendsto_rabs_zero_iff, THEN tendsto_add [OF _ tendsto_const], of "- arctan 1", THEN tendsto_minus]
```
```  3880     have "(?c 1) sums (arctan 1)" unfolding sums_def by auto
```
```  3881     hence "arctan 1 = (\<Sum> i. ?c 1 i)" by (rule sums_unique)
```
```  3882
```
```  3883     show ?thesis
```
```  3884     proof (cases "x = 1")
```
```  3885       case True
```
```  3886       then show ?thesis by (simp add: `arctan 1 = (\<Sum> i. ?c 1 i)`)
```
```  3887     next
```
```  3888       case False
```
```  3889       hence "x = -1" using `\<bar>x\<bar> = 1` by auto
```
```  3890
```
```  3891       have "- (pi / 2) < 0" using pi_gt_zero by auto
```
```  3892       have "- (2 * pi) < 0" using pi_gt_zero by auto
```
```  3893
```
```  3894       have c_minus_minus: "\<And>i. ?c (- 1) i = - ?c 1 i"
```
```  3895         unfolding One_nat_def by auto
```
```  3896
```
```  3897       have "arctan (- 1) = arctan (tan (-(pi / 4)))"
```
```  3898         unfolding tan_45 tan_minus ..
```
```  3899       also have "\<dots> = - (pi / 4)"
```
```  3900         by (rule arctan_tan, auto simp add: order_less_trans[OF `- (pi / 2) < 0` pi_gt_zero])
```
```  3901       also have "\<dots> = - (arctan (tan (pi / 4)))"
```
```  3902         unfolding neg_equal_iff_equal by (rule arctan_tan[symmetric], auto simp add: order_less_trans[OF `- (2 * pi) < 0` pi_gt_zero])
```
```  3903       also have "\<dots> = - (arctan 1)"
```
```  3904         unfolding tan_45 ..
```
```  3905       also have "\<dots> = - (\<Sum> i. ?c 1 i)"
```
```  3906         using `arctan 1 = (\<Sum> i. ?c 1 i)` by auto
```
```  3907       also have "\<dots> = (\<Sum> i. ?c (- 1) i)"
```
```  3908         using suminf_minus[OF sums_summable[OF `(?c 1) sums (arctan 1)`]]
```
```  3909         unfolding c_minus_minus by auto
```
```  3910       finally show ?thesis using `x = -1` by auto
```
```  3911     qed
```
```  3912   qed
```
```  3913 qed
```
```  3914
```
```  3915 lemma arctan_half:
```
```  3916   fixes x :: real
```
```  3917   shows "arctan x = 2 * arctan (x / (1 + sqrt(1 + x\<^sup>2)))"
```
```  3918 proof -
```
```  3919   obtain y where low: "- (pi / 2) < y" and high: "y < pi / 2" and y_eq: "tan y = x"
```
```  3920     using tan_total by blast
```
```  3921   hence low2: "- (pi / 2) < y / 2" and high2: "y / 2 < pi / 2"
```
```  3922     by auto
```
```  3923
```
```  3924   have divide_nonzero_divide: "\<And>A B C :: real. C \<noteq> 0 \<Longrightarrow> A / B = (A / C) / (B / C)"
```
```  3925     by auto
```
```  3926
```
```  3927   have "0 < cos y" using cos_gt_zero_pi[OF low high] .
```
```  3928   hence "cos y \<noteq> 0" and cos_sqrt: "sqrt ((cos y)\<^sup>2) = cos y"
```
```  3929     by auto
```
```  3930
```
```  3931   have "1 + (tan y)\<^sup>2 = 1 + (sin y)\<^sup>2 / (cos y)\<^sup>2"
```
```  3932     unfolding tan_def power_divide ..
```
```  3933   also have "\<dots> = (cos y)\<^sup>2 / (cos y)\<^sup>2 + (sin y)\<^sup>2 / (cos y)\<^sup>2"
```
```  3934     using `cos y \<noteq> 0` by auto
```
```  3935   also have "\<dots> = 1 / (cos y)\<^sup>2"
```
```  3936     unfolding add_divide_distrib[symmetric] sin_cos_squared_add2 ..
```
```  3937   finally have "1 + (tan y)\<^sup>2 = 1 / (cos y)\<^sup>2" .
```
```  3938
```
```  3939   have "sin y / (cos y + 1) = tan y / ((cos y + 1) / cos y)"
```
```  3940     unfolding tan_def divide_nonzero_divide[OF `cos y \<noteq> 0`, symmetric] ..
```
```  3941   also have "\<dots> = tan y / (1 + 1 / cos y)"
```
```  3942     using `cos y \<noteq> 0` unfolding add_divide_distrib by auto
```
```  3943   also have "\<dots> = tan y / (1 + 1 / sqrt ((cos y)\<^sup>2))"
```
```  3944     unfolding cos_sqrt ..
```
```  3945   also have "\<dots> = tan y / (1 + sqrt (1 / (cos y)\<^sup>2))"
```
```  3946     unfolding real_sqrt_divide by auto
```
```  3947   finally have eq: "sin y / (cos y + 1) = tan y / (1 + sqrt(1 + (tan y)\<^sup>2))"
```
```  3948     unfolding `1 + (tan y)\<^sup>2 = 1 / (cos y)\<^sup>2` .
```
```  3949
```
```  3950   have "arctan x = y"
```
```  3951     using arctan_tan low high y_eq by auto
```
```  3952   also have "\<dots> = 2 * (arctan (tan (y/2)))"
```
```  3953     using arctan_tan[OF low2 high2] by auto
```
```  3954   also have "\<dots> = 2 * (arctan (sin y / (cos y + 1)))"
```
```  3955     unfolding tan_half by auto
```
```  3956   finally show ?thesis
```
```  3957     unfolding eq `tan y = x` .
```
```  3958 qed
```
```  3959
```
```  3960 lemma arctan_monotone: "x < y \<Longrightarrow> arctan x < arctan y"
```
```  3961   by (simp only: arctan_less_iff)
```
```  3962
```
```  3963 lemma arctan_monotone': "x \<le> y \<Longrightarrow> arctan x \<le> arctan y"
```
```  3964   by (simp only: arctan_le_iff)
```
```  3965
```
```  3966 lemma arctan_inverse:
```
```  3967   assumes "x \<noteq> 0"
```
```  3968   shows "arctan (1 / x) = sgn x * pi / 2 - arctan x"
```
```  3969 proof (rule arctan_unique)
```
```  3970   show "- (pi / 2) < sgn x * pi / 2 - arctan x"
```
```  3971     using arctan_bounded [of x] assms
```
```  3972     unfolding sgn_real_def
```
```  3973     apply (auto simp add: algebra_simps)
```
```  3974     apply (drule zero_less_arctan_iff [THEN iffD2])
```
```  3975     apply arith
```
```  3976     done
```
```  3977   show "sgn x * pi / 2 - arctan x < pi / 2"
```
```  3978     using arctan_bounded [of "- x"] assms
```
```  3979     unfolding sgn_real_def arctan_minus
```
```  3980     by (auto simp add: algebra_simps)
```
```  3981   show "tan (sgn x * pi / 2 - arctan x) = 1 / x"
```
```  3982     unfolding tan_inverse [of "arctan x", unfolded tan_arctan]
```
```  3983     unfolding sgn_real_def
```
```  3984     by (simp add: tan_def cos_arctan sin_arctan sin_diff cos_diff)
```
```  3985 qed
```
```  3986
```
```  3987 theorem pi_series: "pi / 4 = (\<Sum> k. (-1)^k * 1 / real (k*2+1))" (is "_ = ?SUM")
```
```  3988 proof -
```
```  3989   have "pi / 4 = arctan 1" using arctan_one by auto
```
```  3990   also have "\<dots> = ?SUM" using arctan_series[of 1] by auto
```
```  3991   finally show ?thesis by auto
```
```  3992 qed
```
```  3993
```
```  3994
```
```  3995 subsection {* Existence of Polar Coordinates *}
```
```  3996
```
```  3997 lemma cos_x_y_le_one: "\<bar>x / sqrt (x\<^sup>2 + y\<^sup>2)\<bar> \<le> 1"
```
```  3998   apply (rule power2_le_imp_le [OF _ zero_le_one])
```
```  3999   apply (simp add: power_divide divide_le_eq not_sum_power2_lt_zero)
```
```  4000   done
```
```  4001
```
```  4002 lemma cos_arccos_abs: "\<bar>y\<bar> \<le> 1 \<Longrightarrow> cos (arccos y) = y"
```
```  4003   by (simp add: abs_le_iff)
```
```  4004
```
```  4005 lemma sin_arccos_abs: "\<bar>y\<bar> \<le> 1 \<Longrightarrow> sin (arccos y) = sqrt (1 - y\<^sup>2)"
```
```  4006   by (simp add: sin_arccos abs_le_iff)
```
```  4007
```
```  4008 lemmas cos_arccos_lemma1 = cos_arccos_abs [OF cos_x_y_le_one]
```
```  4009
```
```  4010 lemmas sin_arccos_lemma1 = sin_arccos_abs [OF cos_x_y_le_one]
```
```  4011
```
```  4012 lemma polar_Ex: "\<exists>r a. x = r * cos a & y = r * sin a"
```
```  4013 proof -
```
```  4014   have polar_ex1: "\<And>y. 0 < y \<Longrightarrow> \<exists>r a. x = r * cos a & y = r * sin a"
```
```  4015     apply (rule_tac x = "sqrt (x\<^sup>2 + y\<^sup>2)" in exI)
```
```  4016     apply (rule_tac x = "arccos (x / sqrt (x\<^sup>2 + y\<^sup>2))" in exI)
```
```  4017     apply (simp add: cos_arccos_lemma1 sin_arccos_lemma1 power_divide
```
```  4018                      real_sqrt_mult [symmetric] right_diff_distrib)
```
```  4019     done
```
```  4020   show ?thesis
```
```  4021   proof (cases "0::real" y rule: linorder_cases)
```
```  4022     case less
```
```  4023       then show ?thesis by (rule polar_ex1)
```
```  4024   next
```
```  4025     case equal
```
```  4026       then show ?thesis
```
```  4027         by (force simp add: intro!: cos_zero sin_zero)
```
```  4028   next
```
```  4029     case greater
```
```  4030       then show ?thesis
```
```  4031      using polar_ex1 [where y="-y"]
```
```  4032     by auto (metis cos_minus minus_minus minus_mult_right sin_minus)
```
```  4033   qed
```
```  4034 qed
```
```  4035
```
```  4036 end
```