src/HOL/Rings.thy
 author haftmann Mon Sep 26 07:56:54 2016 +0200 (2016-09-26) changeset 63950 cdc1e59aa513 parent 63947 559f0882d6a6 child 64164 38c407446400 permissions -rw-r--r--
syntactic type class for operation mod named after mod;
simplified assumptions of type class semiring_div
```     1 (*  Title:      HOL/Rings.thy
```
```     2     Author:     Gertrud Bauer
```
```     3     Author:     Steven Obua
```
```     4     Author:     Tobias Nipkow
```
```     5     Author:     Lawrence C Paulson
```
```     6     Author:     Markus Wenzel
```
```     7     Author:     Jeremy Avigad
```
```     8 *)
```
```     9
```
```    10 section \<open>Rings\<close>
```
```    11
```
```    12 theory Rings
```
```    13   imports Groups Set
```
```    14 begin
```
```    15
```
```    16 class semiring = ab_semigroup_add + semigroup_mult +
```
```    17   assumes distrib_right[algebra_simps]: "(a + b) * c = a * c + b * c"
```
```    18   assumes distrib_left[algebra_simps]: "a * (b + c) = a * b + a * c"
```
```    19 begin
```
```    20
```
```    21 text \<open>For the \<open>combine_numerals\<close> simproc\<close>
```
```    22 lemma combine_common_factor: "a * e + (b * e + c) = (a + b) * e + c"
```
```    23   by (simp add: distrib_right ac_simps)
```
```    24
```
```    25 end
```
```    26
```
```    27 class mult_zero = times + zero +
```
```    28   assumes mult_zero_left [simp]: "0 * a = 0"
```
```    29   assumes mult_zero_right [simp]: "a * 0 = 0"
```
```    30 begin
```
```    31
```
```    32 lemma mult_not_zero: "a * b \<noteq> 0 \<Longrightarrow> a \<noteq> 0 \<and> b \<noteq> 0"
```
```    33   by auto
```
```    34
```
```    35 end
```
```    36
```
```    37 class semiring_0 = semiring + comm_monoid_add + mult_zero
```
```    38
```
```    39 class semiring_0_cancel = semiring + cancel_comm_monoid_add
```
```    40 begin
```
```    41
```
```    42 subclass semiring_0
```
```    43 proof
```
```    44   fix a :: 'a
```
```    45   have "0 * a + 0 * a = 0 * a + 0"
```
```    46     by (simp add: distrib_right [symmetric])
```
```    47   then show "0 * a = 0"
```
```    48     by (simp only: add_left_cancel)
```
```    49   have "a * 0 + a * 0 = a * 0 + 0"
```
```    50     by (simp add: distrib_left [symmetric])
```
```    51   then show "a * 0 = 0"
```
```    52     by (simp only: add_left_cancel)
```
```    53 qed
```
```    54
```
```    55 end
```
```    56
```
```    57 class comm_semiring = ab_semigroup_add + ab_semigroup_mult +
```
```    58   assumes distrib: "(a + b) * c = a * c + b * c"
```
```    59 begin
```
```    60
```
```    61 subclass semiring
```
```    62 proof
```
```    63   fix a b c :: 'a
```
```    64   show "(a + b) * c = a * c + b * c"
```
```    65     by (simp add: distrib)
```
```    66   have "a * (b + c) = (b + c) * a"
```
```    67     by (simp add: ac_simps)
```
```    68   also have "\<dots> = b * a + c * a"
```
```    69     by (simp only: distrib)
```
```    70   also have "\<dots> = a * b + a * c"
```
```    71     by (simp add: ac_simps)
```
```    72   finally show "a * (b + c) = a * b + a * c"
```
```    73     by blast
```
```    74 qed
```
```    75
```
```    76 end
```
```    77
```
```    78 class comm_semiring_0 = comm_semiring + comm_monoid_add + mult_zero
```
```    79 begin
```
```    80
```
```    81 subclass semiring_0 ..
```
```    82
```
```    83 end
```
```    84
```
```    85 class comm_semiring_0_cancel = comm_semiring + cancel_comm_monoid_add
```
```    86 begin
```
```    87
```
```    88 subclass semiring_0_cancel ..
```
```    89
```
```    90 subclass comm_semiring_0 ..
```
```    91
```
```    92 end
```
```    93
```
```    94 class zero_neq_one = zero + one +
```
```    95   assumes zero_neq_one [simp]: "0 \<noteq> 1"
```
```    96 begin
```
```    97
```
```    98 lemma one_neq_zero [simp]: "1 \<noteq> 0"
```
```    99   by (rule not_sym) (rule zero_neq_one)
```
```   100
```
```   101 definition of_bool :: "bool \<Rightarrow> 'a"
```
```   102   where "of_bool p = (if p then 1 else 0)"
```
```   103
```
```   104 lemma of_bool_eq [simp, code]:
```
```   105   "of_bool False = 0"
```
```   106   "of_bool True = 1"
```
```   107   by (simp_all add: of_bool_def)
```
```   108
```
```   109 lemma of_bool_eq_iff: "of_bool p = of_bool q \<longleftrightarrow> p = q"
```
```   110   by (simp add: of_bool_def)
```
```   111
```
```   112 lemma split_of_bool [split]: "P (of_bool p) \<longleftrightarrow> (p \<longrightarrow> P 1) \<and> (\<not> p \<longrightarrow> P 0)"
```
```   113   by (cases p) simp_all
```
```   114
```
```   115 lemma split_of_bool_asm: "P (of_bool p) \<longleftrightarrow> \<not> (p \<and> \<not> P 1 \<or> \<not> p \<and> \<not> P 0)"
```
```   116   by (cases p) simp_all
```
```   117
```
```   118 end
```
```   119
```
```   120 class semiring_1 = zero_neq_one + semiring_0 + monoid_mult
```
```   121
```
```   122 text \<open>Abstract divisibility\<close>
```
```   123
```
```   124 class dvd = times
```
```   125 begin
```
```   126
```
```   127 definition dvd :: "'a \<Rightarrow> 'a \<Rightarrow> bool" (infix "dvd" 50)
```
```   128   where "b dvd a \<longleftrightarrow> (\<exists>k. a = b * k)"
```
```   129
```
```   130 lemma dvdI [intro?]: "a = b * k \<Longrightarrow> b dvd a"
```
```   131   unfolding dvd_def ..
```
```   132
```
```   133 lemma dvdE [elim?]: "b dvd a \<Longrightarrow> (\<And>k. a = b * k \<Longrightarrow> P) \<Longrightarrow> P"
```
```   134   unfolding dvd_def by blast
```
```   135
```
```   136 end
```
```   137
```
```   138 context comm_monoid_mult
```
```   139 begin
```
```   140
```
```   141 subclass dvd .
```
```   142
```
```   143 lemma dvd_refl [simp]: "a dvd a"
```
```   144 proof
```
```   145   show "a = a * 1" by simp
```
```   146 qed
```
```   147
```
```   148 lemma dvd_trans [trans]:
```
```   149   assumes "a dvd b" and "b dvd c"
```
```   150   shows "a dvd c"
```
```   151 proof -
```
```   152   from assms obtain v where "b = a * v"
```
```   153     by (auto elim!: dvdE)
```
```   154   moreover from assms obtain w where "c = b * w"
```
```   155     by (auto elim!: dvdE)
```
```   156   ultimately have "c = a * (v * w)"
```
```   157     by (simp add: mult.assoc)
```
```   158   then show ?thesis ..
```
```   159 qed
```
```   160
```
```   161 lemma subset_divisors_dvd: "{c. c dvd a} \<subseteq> {c. c dvd b} \<longleftrightarrow> a dvd b"
```
```   162   by (auto simp add: subset_iff intro: dvd_trans)
```
```   163
```
```   164 lemma strict_subset_divisors_dvd: "{c. c dvd a} \<subset> {c. c dvd b} \<longleftrightarrow> a dvd b \<and> \<not> b dvd a"
```
```   165   by (auto simp add: subset_iff intro: dvd_trans)
```
```   166
```
```   167 lemma one_dvd [simp]: "1 dvd a"
```
```   168   by (auto intro!: dvdI)
```
```   169
```
```   170 lemma dvd_mult [simp]: "a dvd c \<Longrightarrow> a dvd (b * c)"
```
```   171   by (auto intro!: mult.left_commute dvdI elim!: dvdE)
```
```   172
```
```   173 lemma dvd_mult2 [simp]: "a dvd b \<Longrightarrow> a dvd (b * c)"
```
```   174   using dvd_mult [of a b c] by (simp add: ac_simps)
```
```   175
```
```   176 lemma dvd_triv_right [simp]: "a dvd b * a"
```
```   177   by (rule dvd_mult) (rule dvd_refl)
```
```   178
```
```   179 lemma dvd_triv_left [simp]: "a dvd a * b"
```
```   180   by (rule dvd_mult2) (rule dvd_refl)
```
```   181
```
```   182 lemma mult_dvd_mono:
```
```   183   assumes "a dvd b"
```
```   184     and "c dvd d"
```
```   185   shows "a * c dvd b * d"
```
```   186 proof -
```
```   187   from \<open>a dvd b\<close> obtain b' where "b = a * b'" ..
```
```   188   moreover from \<open>c dvd d\<close> obtain d' where "d = c * d'" ..
```
```   189   ultimately have "b * d = (a * c) * (b' * d')"
```
```   190     by (simp add: ac_simps)
```
```   191   then show ?thesis ..
```
```   192 qed
```
```   193
```
```   194 lemma dvd_mult_left: "a * b dvd c \<Longrightarrow> a dvd c"
```
```   195   by (simp add: dvd_def mult.assoc) blast
```
```   196
```
```   197 lemma dvd_mult_right: "a * b dvd c \<Longrightarrow> b dvd c"
```
```   198   using dvd_mult_left [of b a c] by (simp add: ac_simps)
```
```   199
```
```   200 end
```
```   201
```
```   202 class comm_semiring_1 = zero_neq_one + comm_semiring_0 + comm_monoid_mult
```
```   203 begin
```
```   204
```
```   205 subclass semiring_1 ..
```
```   206
```
```   207 lemma dvd_0_left_iff [simp]: "0 dvd a \<longleftrightarrow> a = 0"
```
```   208   by (auto intro: dvd_refl elim!: dvdE)
```
```   209
```
```   210 lemma dvd_0_right [iff]: "a dvd 0"
```
```   211 proof
```
```   212   show "0 = a * 0" by simp
```
```   213 qed
```
```   214
```
```   215 lemma dvd_0_left: "0 dvd a \<Longrightarrow> a = 0"
```
```   216   by simp
```
```   217
```
```   218 lemma dvd_add [simp]:
```
```   219   assumes "a dvd b" and "a dvd c"
```
```   220   shows "a dvd (b + c)"
```
```   221 proof -
```
```   222   from \<open>a dvd b\<close> obtain b' where "b = a * b'" ..
```
```   223   moreover from \<open>a dvd c\<close> obtain c' where "c = a * c'" ..
```
```   224   ultimately have "b + c = a * (b' + c')"
```
```   225     by (simp add: distrib_left)
```
```   226   then show ?thesis ..
```
```   227 qed
```
```   228
```
```   229 end
```
```   230
```
```   231 class semiring_1_cancel = semiring + cancel_comm_monoid_add
```
```   232   + zero_neq_one + monoid_mult
```
```   233 begin
```
```   234
```
```   235 subclass semiring_0_cancel ..
```
```   236
```
```   237 subclass semiring_1 ..
```
```   238
```
```   239 end
```
```   240
```
```   241 class comm_semiring_1_cancel =
```
```   242   comm_semiring + cancel_comm_monoid_add + zero_neq_one + comm_monoid_mult +
```
```   243   assumes right_diff_distrib' [algebra_simps]: "a * (b - c) = a * b - a * c"
```
```   244 begin
```
```   245
```
```   246 subclass semiring_1_cancel ..
```
```   247 subclass comm_semiring_0_cancel ..
```
```   248 subclass comm_semiring_1 ..
```
```   249
```
```   250 lemma left_diff_distrib' [algebra_simps]: "(b - c) * a = b * a - c * a"
```
```   251   by (simp add: algebra_simps)
```
```   252
```
```   253 lemma dvd_add_times_triv_left_iff [simp]: "a dvd c * a + b \<longleftrightarrow> a dvd b"
```
```   254 proof -
```
```   255   have "a dvd a * c + b \<longleftrightarrow> a dvd b" (is "?P \<longleftrightarrow> ?Q")
```
```   256   proof
```
```   257     assume ?Q
```
```   258     then show ?P by simp
```
```   259   next
```
```   260     assume ?P
```
```   261     then obtain d where "a * c + b = a * d" ..
```
```   262     then have "a * c + b - a * c = a * d - a * c" by simp
```
```   263     then have "b = a * d - a * c" by simp
```
```   264     then have "b = a * (d - c)" by (simp add: algebra_simps)
```
```   265     then show ?Q ..
```
```   266   qed
```
```   267   then show "a dvd c * a + b \<longleftrightarrow> a dvd b" by (simp add: ac_simps)
```
```   268 qed
```
```   269
```
```   270 lemma dvd_add_times_triv_right_iff [simp]: "a dvd b + c * a \<longleftrightarrow> a dvd b"
```
```   271   using dvd_add_times_triv_left_iff [of a c b] by (simp add: ac_simps)
```
```   272
```
```   273 lemma dvd_add_triv_left_iff [simp]: "a dvd a + b \<longleftrightarrow> a dvd b"
```
```   274   using dvd_add_times_triv_left_iff [of a 1 b] by simp
```
```   275
```
```   276 lemma dvd_add_triv_right_iff [simp]: "a dvd b + a \<longleftrightarrow> a dvd b"
```
```   277   using dvd_add_times_triv_right_iff [of a b 1] by simp
```
```   278
```
```   279 lemma dvd_add_right_iff:
```
```   280   assumes "a dvd b"
```
```   281   shows "a dvd b + c \<longleftrightarrow> a dvd c" (is "?P \<longleftrightarrow> ?Q")
```
```   282 proof
```
```   283   assume ?P
```
```   284   then obtain d where "b + c = a * d" ..
```
```   285   moreover from \<open>a dvd b\<close> obtain e where "b = a * e" ..
```
```   286   ultimately have "a * e + c = a * d" by simp
```
```   287   then have "a * e + c - a * e = a * d - a * e" by simp
```
```   288   then have "c = a * d - a * e" by simp
```
```   289   then have "c = a * (d - e)" by (simp add: algebra_simps)
```
```   290   then show ?Q ..
```
```   291 next
```
```   292   assume ?Q
```
```   293   with assms show ?P by simp
```
```   294 qed
```
```   295
```
```   296 lemma dvd_add_left_iff: "a dvd c \<Longrightarrow> a dvd b + c \<longleftrightarrow> a dvd b"
```
```   297   using dvd_add_right_iff [of a c b] by (simp add: ac_simps)
```
```   298
```
```   299 end
```
```   300
```
```   301 class ring = semiring + ab_group_add
```
```   302 begin
```
```   303
```
```   304 subclass semiring_0_cancel ..
```
```   305
```
```   306 text \<open>Distribution rules\<close>
```
```   307
```
```   308 lemma minus_mult_left: "- (a * b) = - a * b"
```
```   309   by (rule minus_unique) (simp add: distrib_right [symmetric])
```
```   310
```
```   311 lemma minus_mult_right: "- (a * b) = a * - b"
```
```   312   by (rule minus_unique) (simp add: distrib_left [symmetric])
```
```   313
```
```   314 text \<open>Extract signs from products\<close>
```
```   315 lemmas mult_minus_left [simp] = minus_mult_left [symmetric]
```
```   316 lemmas mult_minus_right [simp] = minus_mult_right [symmetric]
```
```   317
```
```   318 lemma minus_mult_minus [simp]: "- a * - b = a * b"
```
```   319   by simp
```
```   320
```
```   321 lemma minus_mult_commute: "- a * b = a * - b"
```
```   322   by simp
```
```   323
```
```   324 lemma right_diff_distrib [algebra_simps]: "a * (b - c) = a * b - a * c"
```
```   325   using distrib_left [of a b "-c "] by simp
```
```   326
```
```   327 lemma left_diff_distrib [algebra_simps]: "(a - b) * c = a * c - b * c"
```
```   328   using distrib_right [of a "- b" c] by simp
```
```   329
```
```   330 lemmas ring_distribs = distrib_left distrib_right left_diff_distrib right_diff_distrib
```
```   331
```
```   332 lemma eq_add_iff1: "a * e + c = b * e + d \<longleftrightarrow> (a - b) * e + c = d"
```
```   333   by (simp add: algebra_simps)
```
```   334
```
```   335 lemma eq_add_iff2: "a * e + c = b * e + d \<longleftrightarrow> c = (b - a) * e + d"
```
```   336   by (simp add: algebra_simps)
```
```   337
```
```   338 end
```
```   339
```
```   340 lemmas ring_distribs = distrib_left distrib_right left_diff_distrib right_diff_distrib
```
```   341
```
```   342 class comm_ring = comm_semiring + ab_group_add
```
```   343 begin
```
```   344
```
```   345 subclass ring ..
```
```   346 subclass comm_semiring_0_cancel ..
```
```   347
```
```   348 lemma square_diff_square_factored: "x * x - y * y = (x + y) * (x - y)"
```
```   349   by (simp add: algebra_simps)
```
```   350
```
```   351 end
```
```   352
```
```   353 class ring_1 = ring + zero_neq_one + monoid_mult
```
```   354 begin
```
```   355
```
```   356 subclass semiring_1_cancel ..
```
```   357
```
```   358 lemma square_diff_one_factored: "x * x - 1 = (x + 1) * (x - 1)"
```
```   359   by (simp add: algebra_simps)
```
```   360
```
```   361 end
```
```   362
```
```   363 class comm_ring_1 = comm_ring + zero_neq_one + comm_monoid_mult
```
```   364 begin
```
```   365
```
```   366 subclass ring_1 ..
```
```   367 subclass comm_semiring_1_cancel
```
```   368   by unfold_locales (simp add: algebra_simps)
```
```   369
```
```   370 lemma dvd_minus_iff [simp]: "x dvd - y \<longleftrightarrow> x dvd y"
```
```   371 proof
```
```   372   assume "x dvd - y"
```
```   373   then have "x dvd - 1 * - y" by (rule dvd_mult)
```
```   374   then show "x dvd y" by simp
```
```   375 next
```
```   376   assume "x dvd y"
```
```   377   then have "x dvd - 1 * y" by (rule dvd_mult)
```
```   378   then show "x dvd - y" by simp
```
```   379 qed
```
```   380
```
```   381 lemma minus_dvd_iff [simp]: "- x dvd y \<longleftrightarrow> x dvd y"
```
```   382 proof
```
```   383   assume "- x dvd y"
```
```   384   then obtain k where "y = - x * k" ..
```
```   385   then have "y = x * - k" by simp
```
```   386   then show "x dvd y" ..
```
```   387 next
```
```   388   assume "x dvd y"
```
```   389   then obtain k where "y = x * k" ..
```
```   390   then have "y = - x * - k" by simp
```
```   391   then show "- x dvd y" ..
```
```   392 qed
```
```   393
```
```   394 lemma dvd_diff [simp]: "x dvd y \<Longrightarrow> x dvd z \<Longrightarrow> x dvd (y - z)"
```
```   395   using dvd_add [of x y "- z"] by simp
```
```   396
```
```   397 end
```
```   398
```
```   399 class semiring_no_zero_divisors = semiring_0 +
```
```   400   assumes no_zero_divisors: "a \<noteq> 0 \<Longrightarrow> b \<noteq> 0 \<Longrightarrow> a * b \<noteq> 0"
```
```   401 begin
```
```   402
```
```   403 lemma divisors_zero:
```
```   404   assumes "a * b = 0"
```
```   405   shows "a = 0 \<or> b = 0"
```
```   406 proof (rule classical)
```
```   407   assume "\<not> ?thesis"
```
```   408   then have "a \<noteq> 0" and "b \<noteq> 0" by auto
```
```   409   with no_zero_divisors have "a * b \<noteq> 0" by blast
```
```   410   with assms show ?thesis by simp
```
```   411 qed
```
```   412
```
```   413 lemma mult_eq_0_iff [simp]: "a * b = 0 \<longleftrightarrow> a = 0 \<or> b = 0"
```
```   414 proof (cases "a = 0 \<or> b = 0")
```
```   415   case False
```
```   416   then have "a \<noteq> 0" and "b \<noteq> 0" by auto
```
```   417     then show ?thesis using no_zero_divisors by simp
```
```   418 next
```
```   419   case True
```
```   420   then show ?thesis by auto
```
```   421 qed
```
```   422
```
```   423 end
```
```   424
```
```   425 class semiring_1_no_zero_divisors = semiring_1 + semiring_no_zero_divisors
```
```   426
```
```   427 class semiring_no_zero_divisors_cancel = semiring_no_zero_divisors +
```
```   428   assumes mult_cancel_right [simp]: "a * c = b * c \<longleftrightarrow> c = 0 \<or> a = b"
```
```   429     and mult_cancel_left [simp]: "c * a = c * b \<longleftrightarrow> c = 0 \<or> a = b"
```
```   430 begin
```
```   431
```
```   432 lemma mult_left_cancel: "c \<noteq> 0 \<Longrightarrow> c * a = c * b \<longleftrightarrow> a = b"
```
```   433   by simp
```
```   434
```
```   435 lemma mult_right_cancel: "c \<noteq> 0 \<Longrightarrow> a * c = b * c \<longleftrightarrow> a = b"
```
```   436   by simp
```
```   437
```
```   438 end
```
```   439
```
```   440 class ring_no_zero_divisors = ring + semiring_no_zero_divisors
```
```   441 begin
```
```   442
```
```   443 subclass semiring_no_zero_divisors_cancel
```
```   444 proof
```
```   445   fix a b c
```
```   446   have "a * c = b * c \<longleftrightarrow> (a - b) * c = 0"
```
```   447     by (simp add: algebra_simps)
```
```   448   also have "\<dots> \<longleftrightarrow> c = 0 \<or> a = b"
```
```   449     by auto
```
```   450   finally show "a * c = b * c \<longleftrightarrow> c = 0 \<or> a = b" .
```
```   451   have "c * a = c * b \<longleftrightarrow> c * (a - b) = 0"
```
```   452     by (simp add: algebra_simps)
```
```   453   also have "\<dots> \<longleftrightarrow> c = 0 \<or> a = b"
```
```   454     by auto
```
```   455   finally show "c * a = c * b \<longleftrightarrow> c = 0 \<or> a = b" .
```
```   456 qed
```
```   457
```
```   458 end
```
```   459
```
```   460 class ring_1_no_zero_divisors = ring_1 + ring_no_zero_divisors
```
```   461 begin
```
```   462
```
```   463 subclass semiring_1_no_zero_divisors ..
```
```   464
```
```   465 lemma square_eq_1_iff: "x * x = 1 \<longleftrightarrow> x = 1 \<or> x = - 1"
```
```   466 proof -
```
```   467   have "(x - 1) * (x + 1) = x * x - 1"
```
```   468     by (simp add: algebra_simps)
```
```   469   then have "x * x = 1 \<longleftrightarrow> (x - 1) * (x + 1) = 0"
```
```   470     by simp
```
```   471   then show ?thesis
```
```   472     by (simp add: eq_neg_iff_add_eq_0)
```
```   473 qed
```
```   474
```
```   475 lemma mult_cancel_right1 [simp]: "c = b * c \<longleftrightarrow> c = 0 \<or> b = 1"
```
```   476   using mult_cancel_right [of 1 c b] by auto
```
```   477
```
```   478 lemma mult_cancel_right2 [simp]: "a * c = c \<longleftrightarrow> c = 0 \<or> a = 1"
```
```   479   using mult_cancel_right [of a c 1] by simp
```
```   480
```
```   481 lemma mult_cancel_left1 [simp]: "c = c * b \<longleftrightarrow> c = 0 \<or> b = 1"
```
```   482   using mult_cancel_left [of c 1 b] by force
```
```   483
```
```   484 lemma mult_cancel_left2 [simp]: "c * a = c \<longleftrightarrow> c = 0 \<or> a = 1"
```
```   485   using mult_cancel_left [of c a 1] by simp
```
```   486
```
```   487 end
```
```   488
```
```   489 class semidom = comm_semiring_1_cancel + semiring_no_zero_divisors
```
```   490 begin
```
```   491
```
```   492 subclass semiring_1_no_zero_divisors ..
```
```   493
```
```   494 end
```
```   495
```
```   496 class idom = comm_ring_1 + semiring_no_zero_divisors
```
```   497 begin
```
```   498
```
```   499 subclass semidom ..
```
```   500
```
```   501 subclass ring_1_no_zero_divisors ..
```
```   502
```
```   503 lemma dvd_mult_cancel_right [simp]: "a * c dvd b * c \<longleftrightarrow> c = 0 \<or> a dvd b"
```
```   504 proof -
```
```   505   have "a * c dvd b * c \<longleftrightarrow> (\<exists>k. b * c = (a * k) * c)"
```
```   506     unfolding dvd_def by (simp add: ac_simps)
```
```   507   also have "(\<exists>k. b * c = (a * k) * c) \<longleftrightarrow> c = 0 \<or> a dvd b"
```
```   508     unfolding dvd_def by simp
```
```   509   finally show ?thesis .
```
```   510 qed
```
```   511
```
```   512 lemma dvd_mult_cancel_left [simp]: "c * a dvd c * b \<longleftrightarrow> c = 0 \<or> a dvd b"
```
```   513 proof -
```
```   514   have "c * a dvd c * b \<longleftrightarrow> (\<exists>k. b * c = (a * k) * c)"
```
```   515     unfolding dvd_def by (simp add: ac_simps)
```
```   516   also have "(\<exists>k. b * c = (a * k) * c) \<longleftrightarrow> c = 0 \<or> a dvd b"
```
```   517     unfolding dvd_def by simp
```
```   518   finally show ?thesis .
```
```   519 qed
```
```   520
```
```   521 lemma square_eq_iff: "a * a = b * b \<longleftrightarrow> a = b \<or> a = - b"
```
```   522 proof
```
```   523   assume "a * a = b * b"
```
```   524   then have "(a - b) * (a + b) = 0"
```
```   525     by (simp add: algebra_simps)
```
```   526   then show "a = b \<or> a = - b"
```
```   527     by (simp add: eq_neg_iff_add_eq_0)
```
```   528 next
```
```   529   assume "a = b \<or> a = - b"
```
```   530   then show "a * a = b * b" by auto
```
```   531 qed
```
```   532
```
```   533 end
```
```   534
```
```   535 text \<open>
```
```   536   The theory of partially ordered rings is taken from the books:
```
```   537     \<^item> \<^emph>\<open>Lattice Theory\<close> by Garret Birkhoff, American Mathematical Society, 1979
```
```   538     \<^item> \<^emph>\<open>Partially Ordered Algebraic Systems\<close>, Pergamon Press, 1963
```
```   539
```
```   540   Most of the used notions can also be looked up in
```
```   541     \<^item> \<^url>\<open>http://www.mathworld.com\<close> by Eric Weisstein et. al.
```
```   542     \<^item> \<^emph>\<open>Algebra I\<close> by van der Waerden, Springer
```
```   543 \<close>
```
```   544
```
```   545 text \<open>Syntactic division operator\<close>
```
```   546
```
```   547 class divide =
```
```   548   fixes divide :: "'a \<Rightarrow> 'a \<Rightarrow> 'a"  (infixl "div" 70)
```
```   549
```
```   550 setup \<open>Sign.add_const_constraint (@{const_name "divide"}, SOME @{typ "'a \<Rightarrow> 'a \<Rightarrow> 'a"})\<close>
```
```   551
```
```   552 context semiring
```
```   553 begin
```
```   554
```
```   555 lemma [field_simps]:
```
```   556   shows distrib_left_NO_MATCH: "NO_MATCH (x div y) a \<Longrightarrow> a * (b + c) = a * b + a * c"
```
```   557     and distrib_right_NO_MATCH: "NO_MATCH (x div y) c \<Longrightarrow> (a + b) * c = a * c + b * c"
```
```   558   by (rule distrib_left distrib_right)+
```
```   559
```
```   560 end
```
```   561
```
```   562 context ring
```
```   563 begin
```
```   564
```
```   565 lemma [field_simps]:
```
```   566   shows left_diff_distrib_NO_MATCH: "NO_MATCH (x div y) c \<Longrightarrow> (a - b) * c = a * c - b * c"
```
```   567     and right_diff_distrib_NO_MATCH: "NO_MATCH (x div y) a \<Longrightarrow> a * (b - c) = a * b - a * c"
```
```   568   by (rule left_diff_distrib right_diff_distrib)+
```
```   569
```
```   570 end
```
```   571
```
```   572 setup \<open>Sign.add_const_constraint (@{const_name "divide"}, SOME @{typ "'a::divide \<Rightarrow> 'a \<Rightarrow> 'a"})\<close>
```
```   573
```
```   574 text \<open>Syntactic division remainder operator\<close>
```
```   575
```
```   576 class modulo = dvd + divide +
```
```   577   fixes modulo :: "'a \<Rightarrow> 'a \<Rightarrow> 'a"  (infixl "mod" 70)
```
```   578
```
```   579 text \<open>Algebraic classes with division\<close>
```
```   580
```
```   581 class semidom_divide = semidom + divide +
```
```   582   assumes nonzero_mult_divide_cancel_right [simp]: "b \<noteq> 0 \<Longrightarrow> (a * b) div b = a"
```
```   583   assumes divide_zero [simp]: "a div 0 = 0"
```
```   584 begin
```
```   585
```
```   586 lemma nonzero_mult_divide_cancel_left [simp]: "a \<noteq> 0 \<Longrightarrow> (a * b) div a = b"
```
```   587   using nonzero_mult_divide_cancel_right [of a b] by (simp add: ac_simps)
```
```   588
```
```   589 subclass semiring_no_zero_divisors_cancel
```
```   590 proof
```
```   591   show *: "a * c = b * c \<longleftrightarrow> c = 0 \<or> a = b" for a b c
```
```   592   proof (cases "c = 0")
```
```   593     case True
```
```   594     then show ?thesis by simp
```
```   595   next
```
```   596     case False
```
```   597     have "a = b" if "a * c = b * c"
```
```   598     proof -
```
```   599       from that have "a * c div c = b * c div c"
```
```   600         by simp
```
```   601       with False show ?thesis
```
```   602         by simp
```
```   603     qed
```
```   604     then show ?thesis by auto
```
```   605   qed
```
```   606   show "c * a = c * b \<longleftrightarrow> c = 0 \<or> a = b" for a b c
```
```   607     using * [of a c b] by (simp add: ac_simps)
```
```   608 qed
```
```   609
```
```   610 lemma div_self [simp]: "a \<noteq> 0 \<Longrightarrow> a div a = 1"
```
```   611   using nonzero_mult_divide_cancel_left [of a 1] by simp
```
```   612
```
```   613 lemma divide_zero_left [simp]: "0 div a = 0"
```
```   614 proof (cases "a = 0")
```
```   615   case True
```
```   616   then show ?thesis by simp
```
```   617 next
```
```   618   case False
```
```   619   then have "a * 0 div a = 0"
```
```   620     by (rule nonzero_mult_divide_cancel_left)
```
```   621   then show ?thesis by simp
```
```   622 qed
```
```   623
```
```   624 lemma divide_1 [simp]: "a div 1 = a"
```
```   625   using nonzero_mult_divide_cancel_left [of 1 a] by simp
```
```   626
```
```   627 end
```
```   628
```
```   629 class idom_divide = idom + semidom_divide
```
```   630
```
```   631 class algebraic_semidom = semidom_divide
```
```   632 begin
```
```   633
```
```   634 text \<open>
```
```   635   Class @{class algebraic_semidom} enriches a integral domain
```
```   636   by notions from algebra, like units in a ring.
```
```   637   It is a separate class to avoid spoiling fields with notions
```
```   638   which are degenerated there.
```
```   639 \<close>
```
```   640
```
```   641 lemma dvd_times_left_cancel_iff [simp]:
```
```   642   assumes "a \<noteq> 0"
```
```   643   shows "a * b dvd a * c \<longleftrightarrow> b dvd c"
```
```   644     (is "?lhs \<longleftrightarrow> ?rhs")
```
```   645 proof
```
```   646   assume ?lhs
```
```   647   then obtain d where "a * c = a * b * d" ..
```
```   648   with assms have "c = b * d" by (simp add: ac_simps)
```
```   649   then show ?rhs ..
```
```   650 next
```
```   651   assume ?rhs
```
```   652   then obtain d where "c = b * d" ..
```
```   653   then have "a * c = a * b * d" by (simp add: ac_simps)
```
```   654   then show ?lhs ..
```
```   655 qed
```
```   656
```
```   657 lemma dvd_times_right_cancel_iff [simp]:
```
```   658   assumes "a \<noteq> 0"
```
```   659   shows "b * a dvd c * a \<longleftrightarrow> b dvd c"
```
```   660   using dvd_times_left_cancel_iff [of a b c] assms by (simp add: ac_simps)
```
```   661
```
```   662 lemma div_dvd_iff_mult:
```
```   663   assumes "b \<noteq> 0" and "b dvd a"
```
```   664   shows "a div b dvd c \<longleftrightarrow> a dvd c * b"
```
```   665 proof -
```
```   666   from \<open>b dvd a\<close> obtain d where "a = b * d" ..
```
```   667   with \<open>b \<noteq> 0\<close> show ?thesis by (simp add: ac_simps)
```
```   668 qed
```
```   669
```
```   670 lemma dvd_div_iff_mult:
```
```   671   assumes "c \<noteq> 0" and "c dvd b"
```
```   672   shows "a dvd b div c \<longleftrightarrow> a * c dvd b"
```
```   673 proof -
```
```   674   from \<open>c dvd b\<close> obtain d where "b = c * d" ..
```
```   675   with \<open>c \<noteq> 0\<close> show ?thesis by (simp add: mult.commute [of a])
```
```   676 qed
```
```   677
```
```   678 lemma div_dvd_div [simp]:
```
```   679   assumes "a dvd b" and "a dvd c"
```
```   680   shows "b div a dvd c div a \<longleftrightarrow> b dvd c"
```
```   681 proof (cases "a = 0")
```
```   682   case True
```
```   683   with assms show ?thesis by simp
```
```   684 next
```
```   685   case False
```
```   686   moreover from assms obtain k l where "b = a * k" and "c = a * l"
```
```   687     by (auto elim!: dvdE)
```
```   688   ultimately show ?thesis by simp
```
```   689 qed
```
```   690
```
```   691 lemma div_add [simp]:
```
```   692   assumes "c dvd a" and "c dvd b"
```
```   693   shows "(a + b) div c = a div c + b div c"
```
```   694 proof (cases "c = 0")
```
```   695   case True
```
```   696   then show ?thesis by simp
```
```   697 next
```
```   698   case False
```
```   699   moreover from assms obtain k l where "a = c * k" and "b = c * l"
```
```   700     by (auto elim!: dvdE)
```
```   701   moreover have "c * k + c * l = c * (k + l)"
```
```   702     by (simp add: algebra_simps)
```
```   703   ultimately show ?thesis
```
```   704     by simp
```
```   705 qed
```
```   706
```
```   707 lemma div_mult_div_if_dvd:
```
```   708   assumes "b dvd a" and "d dvd c"
```
```   709   shows "(a div b) * (c div d) = (a * c) div (b * d)"
```
```   710 proof (cases "b = 0 \<or> c = 0")
```
```   711   case True
```
```   712   with assms show ?thesis by auto
```
```   713 next
```
```   714   case False
```
```   715   moreover from assms obtain k l where "a = b * k" and "c = d * l"
```
```   716     by (auto elim!: dvdE)
```
```   717   moreover have "b * k * (d * l) div (b * d) = (b * d) * (k * l) div (b * d)"
```
```   718     by (simp add: ac_simps)
```
```   719   ultimately show ?thesis by simp
```
```   720 qed
```
```   721
```
```   722 lemma dvd_div_eq_mult:
```
```   723   assumes "a \<noteq> 0" and "a dvd b"
```
```   724   shows "b div a = c \<longleftrightarrow> b = c * a"
```
```   725     (is "?lhs \<longleftrightarrow> ?rhs")
```
```   726 proof
```
```   727   assume ?rhs
```
```   728   then show ?lhs by (simp add: assms)
```
```   729 next
```
```   730   assume ?lhs
```
```   731   then have "b div a * a = c * a" by simp
```
```   732   moreover from assms have "b div a * a = b"
```
```   733     by (auto elim!: dvdE simp add: ac_simps)
```
```   734   ultimately show ?rhs by simp
```
```   735 qed
```
```   736
```
```   737 lemma dvd_div_mult_self [simp]: "a dvd b \<Longrightarrow> b div a * a = b"
```
```   738   by (cases "a = 0") (auto elim: dvdE simp add: ac_simps)
```
```   739
```
```   740 lemma dvd_mult_div_cancel [simp]: "a dvd b \<Longrightarrow> a * (b div a) = b"
```
```   741   using dvd_div_mult_self [of a b] by (simp add: ac_simps)
```
```   742
```
```   743 lemma div_mult_swap:
```
```   744   assumes "c dvd b"
```
```   745   shows "a * (b div c) = (a * b) div c"
```
```   746 proof (cases "c = 0")
```
```   747   case True
```
```   748   then show ?thesis by simp
```
```   749 next
```
```   750   case False
```
```   751   from assms obtain d where "b = c * d" ..
```
```   752   moreover from False have "a * divide (d * c) c = ((a * d) * c) div c"
```
```   753     by simp
```
```   754   ultimately show ?thesis by (simp add: ac_simps)
```
```   755 qed
```
```   756
```
```   757 lemma dvd_div_mult: "c dvd b \<Longrightarrow> b div c * a = (b * a) div c"
```
```   758   using div_mult_swap [of c b a] by (simp add: ac_simps)
```
```   759
```
```   760 lemma dvd_div_mult2_eq:
```
```   761   assumes "b * c dvd a"
```
```   762   shows "a div (b * c) = a div b div c"
```
```   763 proof -
```
```   764   from assms obtain k where "a = b * c * k" ..
```
```   765   then show ?thesis
```
```   766     by (cases "b = 0 \<or> c = 0") (auto, simp add: ac_simps)
```
```   767 qed
```
```   768
```
```   769 lemma dvd_div_div_eq_mult:
```
```   770   assumes "a \<noteq> 0" "c \<noteq> 0" and "a dvd b" "c dvd d"
```
```   771   shows "b div a = d div c \<longleftrightarrow> b * c = a * d"
```
```   772     (is "?lhs \<longleftrightarrow> ?rhs")
```
```   773 proof -
```
```   774   from assms have "a * c \<noteq> 0" by simp
```
```   775   then have "?lhs \<longleftrightarrow> b div a * (a * c) = d div c * (a * c)"
```
```   776     by simp
```
```   777   also have "\<dots> \<longleftrightarrow> (a * (b div a)) * c = (c * (d div c)) * a"
```
```   778     by (simp add: ac_simps)
```
```   779   also have "\<dots> \<longleftrightarrow> (a * b div a) * c = (c * d div c) * a"
```
```   780     using assms by (simp add: div_mult_swap)
```
```   781   also have "\<dots> \<longleftrightarrow> ?rhs"
```
```   782     using assms by (simp add: ac_simps)
```
```   783   finally show ?thesis .
```
```   784 qed
```
```   785
```
```   786 lemma dvd_mult_imp_div:
```
```   787   assumes "a * c dvd b"
```
```   788   shows "a dvd b div c"
```
```   789 proof (cases "c = 0")
```
```   790   case True then show ?thesis by simp
```
```   791 next
```
```   792   case False
```
```   793   from \<open>a * c dvd b\<close> obtain d where "b = a * c * d" ..
```
```   794   with False show ?thesis
```
```   795     by (simp add: mult.commute [of a] mult.assoc)
```
```   796 qed
```
```   797
```
```   798
```
```   799 text \<open>Units: invertible elements in a ring\<close>
```
```   800
```
```   801 abbreviation is_unit :: "'a \<Rightarrow> bool"
```
```   802   where "is_unit a \<equiv> a dvd 1"
```
```   803
```
```   804 lemma not_is_unit_0 [simp]: "\<not> is_unit 0"
```
```   805   by simp
```
```   806
```
```   807 lemma unit_imp_dvd [dest]: "is_unit b \<Longrightarrow> b dvd a"
```
```   808   by (rule dvd_trans [of _ 1]) simp_all
```
```   809
```
```   810 lemma unit_dvdE:
```
```   811   assumes "is_unit a"
```
```   812   obtains c where "a \<noteq> 0" and "b = a * c"
```
```   813 proof -
```
```   814   from assms have "a dvd b" by auto
```
```   815   then obtain c where "b = a * c" ..
```
```   816   moreover from assms have "a \<noteq> 0" by auto
```
```   817   ultimately show thesis using that by blast
```
```   818 qed
```
```   819
```
```   820 lemma dvd_unit_imp_unit: "a dvd b \<Longrightarrow> is_unit b \<Longrightarrow> is_unit a"
```
```   821   by (rule dvd_trans)
```
```   822
```
```   823 lemma unit_div_1_unit [simp, intro]:
```
```   824   assumes "is_unit a"
```
```   825   shows "is_unit (1 div a)"
```
```   826 proof -
```
```   827   from assms have "1 = 1 div a * a" by simp
```
```   828   then show "is_unit (1 div a)" by (rule dvdI)
```
```   829 qed
```
```   830
```
```   831 lemma is_unitE [elim?]:
```
```   832   assumes "is_unit a"
```
```   833   obtains b where "a \<noteq> 0" and "b \<noteq> 0"
```
```   834     and "is_unit b" and "1 div a = b" and "1 div b = a"
```
```   835     and "a * b = 1" and "c div a = c * b"
```
```   836 proof (rule that)
```
```   837   define b where "b = 1 div a"
```
```   838   then show "1 div a = b" by simp
```
```   839   from assms b_def show "is_unit b" by simp
```
```   840   with assms show "a \<noteq> 0" and "b \<noteq> 0" by auto
```
```   841   from assms b_def show "a * b = 1" by simp
```
```   842   then have "1 = a * b" ..
```
```   843   with b_def \<open>b \<noteq> 0\<close> show "1 div b = a" by simp
```
```   844   from assms have "a dvd c" ..
```
```   845   then obtain d where "c = a * d" ..
```
```   846   with \<open>a \<noteq> 0\<close> \<open>a * b = 1\<close> show "c div a = c * b"
```
```   847     by (simp add: mult.assoc mult.left_commute [of a])
```
```   848 qed
```
```   849
```
```   850 lemma unit_prod [intro]: "is_unit a \<Longrightarrow> is_unit b \<Longrightarrow> is_unit (a * b)"
```
```   851   by (subst mult_1_left [of 1, symmetric]) (rule mult_dvd_mono)
```
```   852
```
```   853 lemma is_unit_mult_iff: "is_unit (a * b) \<longleftrightarrow> is_unit a \<and> is_unit b"
```
```   854   by (auto dest: dvd_mult_left dvd_mult_right)
```
```   855
```
```   856 lemma unit_div [intro]: "is_unit a \<Longrightarrow> is_unit b \<Longrightarrow> is_unit (a div b)"
```
```   857   by (erule is_unitE [of b a]) (simp add: ac_simps unit_prod)
```
```   858
```
```   859 lemma mult_unit_dvd_iff:
```
```   860   assumes "is_unit b"
```
```   861   shows "a * b dvd c \<longleftrightarrow> a dvd c"
```
```   862 proof
```
```   863   assume "a * b dvd c"
```
```   864   with assms show "a dvd c"
```
```   865     by (simp add: dvd_mult_left)
```
```   866 next
```
```   867   assume "a dvd c"
```
```   868   then obtain k where "c = a * k" ..
```
```   869   with assms have "c = (a * b) * (1 div b * k)"
```
```   870     by (simp add: mult_ac)
```
```   871   then show "a * b dvd c" by (rule dvdI)
```
```   872 qed
```
```   873
```
```   874 lemma mult_unit_dvd_iff': "is_unit a \<Longrightarrow> (a * b) dvd c \<longleftrightarrow> b dvd c"
```
```   875   using mult_unit_dvd_iff [of a b c] by (simp add: ac_simps)
```
```   876
```
```   877 lemma dvd_mult_unit_iff:
```
```   878   assumes "is_unit b"
```
```   879   shows "a dvd c * b \<longleftrightarrow> a dvd c"
```
```   880 proof
```
```   881   assume "a dvd c * b"
```
```   882   with assms have "c * b dvd c * (b * (1 div b))"
```
```   883     by (subst mult_assoc [symmetric]) simp
```
```   884   also from assms have "b * (1 div b) = 1"
```
```   885     by (rule is_unitE) simp
```
```   886   finally have "c * b dvd c" by simp
```
```   887   with \<open>a dvd c * b\<close> show "a dvd c" by (rule dvd_trans)
```
```   888 next
```
```   889   assume "a dvd c"
```
```   890   then show "a dvd c * b" by simp
```
```   891 qed
```
```   892
```
```   893 lemma dvd_mult_unit_iff': "is_unit b \<Longrightarrow> a dvd b * c \<longleftrightarrow> a dvd c"
```
```   894   using dvd_mult_unit_iff [of b a c] by (simp add: ac_simps)
```
```   895
```
```   896 lemma div_unit_dvd_iff: "is_unit b \<Longrightarrow> a div b dvd c \<longleftrightarrow> a dvd c"
```
```   897   by (erule is_unitE [of _ a]) (auto simp add: mult_unit_dvd_iff)
```
```   898
```
```   899 lemma dvd_div_unit_iff: "is_unit b \<Longrightarrow> a dvd c div b \<longleftrightarrow> a dvd c"
```
```   900   by (erule is_unitE [of _ c]) (simp add: dvd_mult_unit_iff)
```
```   901
```
```   902 lemmas unit_dvd_iff = mult_unit_dvd_iff mult_unit_dvd_iff'
```
```   903   dvd_mult_unit_iff dvd_mult_unit_iff'
```
```   904   div_unit_dvd_iff dvd_div_unit_iff (* FIXME consider named_theorems *)
```
```   905
```
```   906 lemma unit_mult_div_div [simp]: "is_unit a \<Longrightarrow> b * (1 div a) = b div a"
```
```   907   by (erule is_unitE [of _ b]) simp
```
```   908
```
```   909 lemma unit_div_mult_self [simp]: "is_unit a \<Longrightarrow> b div a * a = b"
```
```   910   by (rule dvd_div_mult_self) auto
```
```   911
```
```   912 lemma unit_div_1_div_1 [simp]: "is_unit a \<Longrightarrow> 1 div (1 div a) = a"
```
```   913   by (erule is_unitE) simp
```
```   914
```
```   915 lemma unit_div_mult_swap: "is_unit c \<Longrightarrow> a * (b div c) = (a * b) div c"
```
```   916   by (erule unit_dvdE [of _ b]) (simp add: mult.left_commute [of _ c])
```
```   917
```
```   918 lemma unit_div_commute: "is_unit b \<Longrightarrow> (a div b) * c = (a * c) div b"
```
```   919   using unit_div_mult_swap [of b c a] by (simp add: ac_simps)
```
```   920
```
```   921 lemma unit_eq_div1: "is_unit b \<Longrightarrow> a div b = c \<longleftrightarrow> a = c * b"
```
```   922   by (auto elim: is_unitE)
```
```   923
```
```   924 lemma unit_eq_div2: "is_unit b \<Longrightarrow> a = c div b \<longleftrightarrow> a * b = c"
```
```   925   using unit_eq_div1 [of b c a] by auto
```
```   926
```
```   927 lemma unit_mult_left_cancel: "is_unit a \<Longrightarrow> a * b = a * c \<longleftrightarrow> b = c"
```
```   928   using mult_cancel_left [of a b c] by auto
```
```   929
```
```   930 lemma unit_mult_right_cancel: "is_unit a \<Longrightarrow> b * a = c * a \<longleftrightarrow> b = c"
```
```   931   using unit_mult_left_cancel [of a b c] by (auto simp add: ac_simps)
```
```   932
```
```   933 lemma unit_div_cancel:
```
```   934   assumes "is_unit a"
```
```   935   shows "b div a = c div a \<longleftrightarrow> b = c"
```
```   936 proof -
```
```   937   from assms have "is_unit (1 div a)" by simp
```
```   938   then have "b * (1 div a) = c * (1 div a) \<longleftrightarrow> b = c"
```
```   939     by (rule unit_mult_right_cancel)
```
```   940   with assms show ?thesis by simp
```
```   941 qed
```
```   942
```
```   943 lemma is_unit_div_mult2_eq:
```
```   944   assumes "is_unit b" and "is_unit c"
```
```   945   shows "a div (b * c) = a div b div c"
```
```   946 proof -
```
```   947   from assms have "is_unit (b * c)"
```
```   948     by (simp add: unit_prod)
```
```   949   then have "b * c dvd a"
```
```   950     by (rule unit_imp_dvd)
```
```   951   then show ?thesis
```
```   952     by (rule dvd_div_mult2_eq)
```
```   953 qed
```
```   954
```
```   955 lemmas unit_simps = mult_unit_dvd_iff div_unit_dvd_iff dvd_mult_unit_iff
```
```   956   dvd_div_unit_iff unit_div_mult_swap unit_div_commute
```
```   957   unit_mult_left_cancel unit_mult_right_cancel unit_div_cancel
```
```   958   unit_eq_div1 unit_eq_div2
```
```   959
```
```   960 lemma is_unit_divide_mult_cancel_left:
```
```   961   assumes "a \<noteq> 0" and "is_unit b"
```
```   962   shows "a div (a * b) = 1 div b"
```
```   963 proof -
```
```   964   from assms have "a div (a * b) = a div a div b"
```
```   965     by (simp add: mult_unit_dvd_iff dvd_div_mult2_eq)
```
```   966   with assms show ?thesis by simp
```
```   967 qed
```
```   968
```
```   969 lemma is_unit_divide_mult_cancel_right:
```
```   970   assumes "a \<noteq> 0" and "is_unit b"
```
```   971   shows "a div (b * a) = 1 div b"
```
```   972   using assms is_unit_divide_mult_cancel_left [of a b] by (simp add: ac_simps)
```
```   973
```
```   974 end
```
```   975
```
```   976 class normalization_semidom = algebraic_semidom +
```
```   977   fixes normalize :: "'a \<Rightarrow> 'a"
```
```   978     and unit_factor :: "'a \<Rightarrow> 'a"
```
```   979   assumes unit_factor_mult_normalize [simp]: "unit_factor a * normalize a = a"
```
```   980     and normalize_0 [simp]: "normalize 0 = 0"
```
```   981     and unit_factor_0 [simp]: "unit_factor 0 = 0"
```
```   982     and is_unit_normalize: "is_unit a  \<Longrightarrow> normalize a = 1"
```
```   983     and unit_factor_is_unit [iff]: "a \<noteq> 0 \<Longrightarrow> is_unit (unit_factor a)"
```
```   984     and unit_factor_mult: "unit_factor (a * b) = unit_factor a * unit_factor b"
```
```   985 begin
```
```   986
```
```   987 text \<open>
```
```   988   Class @{class normalization_semidom} cultivates the idea that each integral
```
```   989   domain can be split into equivalence classes whose representants are
```
```   990   associated, i.e. divide each other. @{const normalize} specifies a canonical
```
```   991   representant for each equivalence class. The rationale behind this is that
```
```   992   it is easier to reason about equality than equivalences, hence we prefer to
```
```   993   think about equality of normalized values rather than associated elements.
```
```   994 \<close>
```
```   995
```
```   996 lemma unit_factor_dvd [simp]: "a \<noteq> 0 \<Longrightarrow> unit_factor a dvd b"
```
```   997   by (rule unit_imp_dvd) simp
```
```   998
```
```   999 lemma unit_factor_self [simp]: "unit_factor a dvd a"
```
```  1000   by (cases "a = 0") simp_all
```
```  1001
```
```  1002 lemma normalize_mult_unit_factor [simp]: "normalize a * unit_factor a = a"
```
```  1003   using unit_factor_mult_normalize [of a] by (simp add: ac_simps)
```
```  1004
```
```  1005 lemma normalize_eq_0_iff [simp]: "normalize a = 0 \<longleftrightarrow> a = 0"
```
```  1006   (is "?lhs \<longleftrightarrow> ?rhs")
```
```  1007 proof
```
```  1008   assume ?lhs
```
```  1009   moreover have "unit_factor a * normalize a = a" by simp
```
```  1010   ultimately show ?rhs by simp
```
```  1011 next
```
```  1012   assume ?rhs
```
```  1013   then show ?lhs by simp
```
```  1014 qed
```
```  1015
```
```  1016 lemma unit_factor_eq_0_iff [simp]: "unit_factor a = 0 \<longleftrightarrow> a = 0"
```
```  1017   (is "?lhs \<longleftrightarrow> ?rhs")
```
```  1018 proof
```
```  1019   assume ?lhs
```
```  1020   moreover have "unit_factor a * normalize a = a" by simp
```
```  1021   ultimately show ?rhs by simp
```
```  1022 next
```
```  1023   assume ?rhs
```
```  1024   then show ?lhs by simp
```
```  1025 qed
```
```  1026
```
```  1027 lemma is_unit_unit_factor:
```
```  1028   assumes "is_unit a"
```
```  1029   shows "unit_factor a = a"
```
```  1030 proof -
```
```  1031   from assms have "normalize a = 1" by (rule is_unit_normalize)
```
```  1032   moreover from unit_factor_mult_normalize have "unit_factor a * normalize a = a" .
```
```  1033   ultimately show ?thesis by simp
```
```  1034 qed
```
```  1035
```
```  1036 lemma unit_factor_1 [simp]: "unit_factor 1 = 1"
```
```  1037   by (rule is_unit_unit_factor) simp
```
```  1038
```
```  1039 lemma normalize_1 [simp]: "normalize 1 = 1"
```
```  1040   by (rule is_unit_normalize) simp
```
```  1041
```
```  1042 lemma normalize_1_iff: "normalize a = 1 \<longleftrightarrow> is_unit a"
```
```  1043   (is "?lhs \<longleftrightarrow> ?rhs")
```
```  1044 proof
```
```  1045   assume ?rhs
```
```  1046   then show ?lhs by (rule is_unit_normalize)
```
```  1047 next
```
```  1048   assume ?lhs
```
```  1049   then have "unit_factor a * normalize a = unit_factor a * 1"
```
```  1050     by simp
```
```  1051   then have "unit_factor a = a"
```
```  1052     by simp
```
```  1053   moreover
```
```  1054   from \<open>?lhs\<close> have "a \<noteq> 0" by auto
```
```  1055   then have "is_unit (unit_factor a)" by simp
```
```  1056   ultimately show ?rhs by simp
```
```  1057 qed
```
```  1058
```
```  1059 lemma div_normalize [simp]: "a div normalize a = unit_factor a"
```
```  1060 proof (cases "a = 0")
```
```  1061   case True
```
```  1062   then show ?thesis by simp
```
```  1063 next
```
```  1064   case False
```
```  1065   then have "normalize a \<noteq> 0" by simp
```
```  1066   with nonzero_mult_divide_cancel_right
```
```  1067   have "unit_factor a * normalize a div normalize a = unit_factor a" by blast
```
```  1068   then show ?thesis by simp
```
```  1069 qed
```
```  1070
```
```  1071 lemma div_unit_factor [simp]: "a div unit_factor a = normalize a"
```
```  1072 proof (cases "a = 0")
```
```  1073   case True
```
```  1074   then show ?thesis by simp
```
```  1075 next
```
```  1076   case False
```
```  1077   then have "unit_factor a \<noteq> 0" by simp
```
```  1078   with nonzero_mult_divide_cancel_left
```
```  1079   have "unit_factor a * normalize a div unit_factor a = normalize a"
```
```  1080     by blast
```
```  1081   then show ?thesis by simp
```
```  1082 qed
```
```  1083
```
```  1084 lemma normalize_div [simp]: "normalize a div a = 1 div unit_factor a"
```
```  1085 proof (cases "a = 0")
```
```  1086   case True
```
```  1087   then show ?thesis by simp
```
```  1088 next
```
```  1089   case False
```
```  1090   have "normalize a div a = normalize a div (unit_factor a * normalize a)"
```
```  1091     by simp
```
```  1092   also have "\<dots> = 1 div unit_factor a"
```
```  1093     using False by (subst is_unit_divide_mult_cancel_right) simp_all
```
```  1094   finally show ?thesis .
```
```  1095 qed
```
```  1096
```
```  1097 lemma mult_one_div_unit_factor [simp]: "a * (1 div unit_factor b) = a div unit_factor b"
```
```  1098   by (cases "b = 0") simp_all
```
```  1099
```
```  1100 lemma inv_unit_factor_eq_0_iff [simp]:
```
```  1101   "1 div unit_factor a = 0 \<longleftrightarrow> a = 0"
```
```  1102   (is "?lhs \<longleftrightarrow> ?rhs")
```
```  1103 proof
```
```  1104   assume ?lhs
```
```  1105   then have "a * (1 div unit_factor a) = a * 0"
```
```  1106     by simp
```
```  1107   then show ?rhs
```
```  1108     by simp
```
```  1109 next
```
```  1110   assume ?rhs
```
```  1111   then show ?lhs by simp
```
```  1112 qed
```
```  1113
```
```  1114 lemma normalize_mult: "normalize (a * b) = normalize a * normalize b"
```
```  1115 proof (cases "a = 0 \<or> b = 0")
```
```  1116   case True
```
```  1117   then show ?thesis by auto
```
```  1118 next
```
```  1119   case False
```
```  1120   have "unit_factor (a * b) * normalize (a * b) = a * b"
```
```  1121     by (rule unit_factor_mult_normalize)
```
```  1122   then have "normalize (a * b) = a * b div unit_factor (a * b)"
```
```  1123     by simp
```
```  1124   also have "\<dots> = a * b div unit_factor (b * a)"
```
```  1125     by (simp add: ac_simps)
```
```  1126   also have "\<dots> = a * b div unit_factor b div unit_factor a"
```
```  1127     using False by (simp add: unit_factor_mult is_unit_div_mult2_eq [symmetric])
```
```  1128   also have "\<dots> = a * (b div unit_factor b) div unit_factor a"
```
```  1129     using False by (subst unit_div_mult_swap) simp_all
```
```  1130   also have "\<dots> = normalize a * normalize b"
```
```  1131     using False
```
```  1132     by (simp add: mult.commute [of a] mult.commute [of "normalize a"] unit_div_mult_swap [symmetric])
```
```  1133   finally show ?thesis .
```
```  1134 qed
```
```  1135
```
```  1136 lemma unit_factor_idem [simp]: "unit_factor (unit_factor a) = unit_factor a"
```
```  1137   by (cases "a = 0") (auto intro: is_unit_unit_factor)
```
```  1138
```
```  1139 lemma normalize_unit_factor [simp]: "a \<noteq> 0 \<Longrightarrow> normalize (unit_factor a) = 1"
```
```  1140   by (rule is_unit_normalize) simp
```
```  1141
```
```  1142 lemma normalize_idem [simp]: "normalize (normalize a) = normalize a"
```
```  1143 proof (cases "a = 0")
```
```  1144   case True
```
```  1145   then show ?thesis by simp
```
```  1146 next
```
```  1147   case False
```
```  1148   have "normalize a = normalize (unit_factor a * normalize a)"
```
```  1149     by simp
```
```  1150   also have "\<dots> = normalize (unit_factor a) * normalize (normalize a)"
```
```  1151     by (simp only: normalize_mult)
```
```  1152   finally show ?thesis
```
```  1153     using False by simp_all
```
```  1154 qed
```
```  1155
```
```  1156 lemma unit_factor_normalize [simp]:
```
```  1157   assumes "a \<noteq> 0"
```
```  1158   shows "unit_factor (normalize a) = 1"
```
```  1159 proof -
```
```  1160   from assms have *: "normalize a \<noteq> 0"
```
```  1161     by simp
```
```  1162   have "unit_factor (normalize a) * normalize (normalize a) = normalize a"
```
```  1163     by (simp only: unit_factor_mult_normalize)
```
```  1164   then have "unit_factor (normalize a) * normalize a = normalize a"
```
```  1165     by simp
```
```  1166   with * have "unit_factor (normalize a) * normalize a div normalize a = normalize a div normalize a"
```
```  1167     by simp
```
```  1168   with * show ?thesis
```
```  1169     by simp
```
```  1170 qed
```
```  1171
```
```  1172 lemma dvd_unit_factor_div:
```
```  1173   assumes "b dvd a"
```
```  1174   shows "unit_factor (a div b) = unit_factor a div unit_factor b"
```
```  1175 proof -
```
```  1176   from assms have "a = a div b * b"
```
```  1177     by simp
```
```  1178   then have "unit_factor a = unit_factor (a div b * b)"
```
```  1179     by simp
```
```  1180   then show ?thesis
```
```  1181     by (cases "b = 0") (simp_all add: unit_factor_mult)
```
```  1182 qed
```
```  1183
```
```  1184 lemma dvd_normalize_div:
```
```  1185   assumes "b dvd a"
```
```  1186   shows "normalize (a div b) = normalize a div normalize b"
```
```  1187 proof -
```
```  1188   from assms have "a = a div b * b"
```
```  1189     by simp
```
```  1190   then have "normalize a = normalize (a div b * b)"
```
```  1191     by simp
```
```  1192   then show ?thesis
```
```  1193     by (cases "b = 0") (simp_all add: normalize_mult)
```
```  1194 qed
```
```  1195
```
```  1196 lemma normalize_dvd_iff [simp]: "normalize a dvd b \<longleftrightarrow> a dvd b"
```
```  1197 proof -
```
```  1198   have "normalize a dvd b \<longleftrightarrow> unit_factor a * normalize a dvd b"
```
```  1199     using mult_unit_dvd_iff [of "unit_factor a" "normalize a" b]
```
```  1200       by (cases "a = 0") simp_all
```
```  1201   then show ?thesis by simp
```
```  1202 qed
```
```  1203
```
```  1204 lemma dvd_normalize_iff [simp]: "a dvd normalize b \<longleftrightarrow> a dvd b"
```
```  1205 proof -
```
```  1206   have "a dvd normalize  b \<longleftrightarrow> a dvd normalize b * unit_factor b"
```
```  1207     using dvd_mult_unit_iff [of "unit_factor b" a "normalize b"]
```
```  1208       by (cases "b = 0") simp_all
```
```  1209   then show ?thesis by simp
```
```  1210 qed
```
```  1211
```
```  1212 text \<open>
```
```  1213   We avoid an explicit definition of associated elements but prefer explicit
```
```  1214   normalisation instead. In theory we could define an abbreviation like @{prop
```
```  1215   "associated a b \<longleftrightarrow> normalize a = normalize b"} but this is counterproductive
```
```  1216   without suggestive infix syntax, which we do not want to sacrifice for this
```
```  1217   purpose here.
```
```  1218 \<close>
```
```  1219
```
```  1220 lemma associatedI:
```
```  1221   assumes "a dvd b" and "b dvd a"
```
```  1222   shows "normalize a = normalize b"
```
```  1223 proof (cases "a = 0 \<or> b = 0")
```
```  1224   case True
```
```  1225   with assms show ?thesis by auto
```
```  1226 next
```
```  1227   case False
```
```  1228   from \<open>a dvd b\<close> obtain c where b: "b = a * c" ..
```
```  1229   moreover from \<open>b dvd a\<close> obtain d where a: "a = b * d" ..
```
```  1230   ultimately have "b * 1 = b * (c * d)"
```
```  1231     by (simp add: ac_simps)
```
```  1232   with False have "1 = c * d"
```
```  1233     unfolding mult_cancel_left by simp
```
```  1234   then have "is_unit c" and "is_unit d"
```
```  1235     by auto
```
```  1236   with a b show ?thesis
```
```  1237     by (simp add: normalize_mult is_unit_normalize)
```
```  1238 qed
```
```  1239
```
```  1240 lemma associatedD1: "normalize a = normalize b \<Longrightarrow> a dvd b"
```
```  1241   using dvd_normalize_iff [of _ b, symmetric] normalize_dvd_iff [of a _, symmetric]
```
```  1242   by simp
```
```  1243
```
```  1244 lemma associatedD2: "normalize a = normalize b \<Longrightarrow> b dvd a"
```
```  1245   using dvd_normalize_iff [of _ a, symmetric] normalize_dvd_iff [of b _, symmetric]
```
```  1246   by simp
```
```  1247
```
```  1248 lemma associated_unit: "normalize a = normalize b \<Longrightarrow> is_unit a \<Longrightarrow> is_unit b"
```
```  1249   using dvd_unit_imp_unit by (auto dest!: associatedD1 associatedD2)
```
```  1250
```
```  1251 lemma associated_iff_dvd: "normalize a = normalize b \<longleftrightarrow> a dvd b \<and> b dvd a"
```
```  1252   (is "?lhs \<longleftrightarrow> ?rhs")
```
```  1253 proof
```
```  1254   assume ?rhs
```
```  1255   then show ?lhs by (auto intro!: associatedI)
```
```  1256 next
```
```  1257   assume ?lhs
```
```  1258   then have "unit_factor a * normalize a = unit_factor a * normalize b"
```
```  1259     by simp
```
```  1260   then have *: "normalize b * unit_factor a = a"
```
```  1261     by (simp add: ac_simps)
```
```  1262   show ?rhs
```
```  1263   proof (cases "a = 0 \<or> b = 0")
```
```  1264     case True
```
```  1265     with \<open>?lhs\<close> show ?thesis by auto
```
```  1266   next
```
```  1267     case False
```
```  1268     then have "b dvd normalize b * unit_factor a" and "normalize b * unit_factor a dvd b"
```
```  1269       by (simp_all add: mult_unit_dvd_iff dvd_mult_unit_iff)
```
```  1270     with * show ?thesis by simp
```
```  1271   qed
```
```  1272 qed
```
```  1273
```
```  1274 lemma associated_eqI:
```
```  1275   assumes "a dvd b" and "b dvd a"
```
```  1276   assumes "normalize a = a" and "normalize b = b"
```
```  1277   shows "a = b"
```
```  1278 proof -
```
```  1279   from assms have "normalize a = normalize b"
```
```  1280     unfolding associated_iff_dvd by simp
```
```  1281   with \<open>normalize a = a\<close> have "a = normalize b"
```
```  1282     by simp
```
```  1283   with \<open>normalize b = b\<close> show "a = b"
```
```  1284     by simp
```
```  1285 qed
```
```  1286
```
```  1287 end
```
```  1288
```
```  1289 class ordered_semiring = semiring + ordered_comm_monoid_add +
```
```  1290   assumes mult_left_mono: "a \<le> b \<Longrightarrow> 0 \<le> c \<Longrightarrow> c * a \<le> c * b"
```
```  1291   assumes mult_right_mono: "a \<le> b \<Longrightarrow> 0 \<le> c \<Longrightarrow> a * c \<le> b * c"
```
```  1292 begin
```
```  1293
```
```  1294 lemma mult_mono: "a \<le> b \<Longrightarrow> c \<le> d \<Longrightarrow> 0 \<le> b \<Longrightarrow> 0 \<le> c \<Longrightarrow> a * c \<le> b * d"
```
```  1295   apply (erule (1) mult_right_mono [THEN order_trans])
```
```  1296   apply (erule (1) mult_left_mono)
```
```  1297   done
```
```  1298
```
```  1299 lemma mult_mono': "a \<le> b \<Longrightarrow> c \<le> d \<Longrightarrow> 0 \<le> a \<Longrightarrow> 0 \<le> c \<Longrightarrow> a * c \<le> b * d"
```
```  1300   by (rule mult_mono) (fast intro: order_trans)+
```
```  1301
```
```  1302 end
```
```  1303
```
```  1304 class ordered_semiring_0 = semiring_0 + ordered_semiring
```
```  1305 begin
```
```  1306
```
```  1307 lemma mult_nonneg_nonneg [simp]: "0 \<le> a \<Longrightarrow> 0 \<le> b \<Longrightarrow> 0 \<le> a * b"
```
```  1308   using mult_left_mono [of 0 b a] by simp
```
```  1309
```
```  1310 lemma mult_nonneg_nonpos: "0 \<le> a \<Longrightarrow> b \<le> 0 \<Longrightarrow> a * b \<le> 0"
```
```  1311   using mult_left_mono [of b 0 a] by simp
```
```  1312
```
```  1313 lemma mult_nonpos_nonneg: "a \<le> 0 \<Longrightarrow> 0 \<le> b \<Longrightarrow> a * b \<le> 0"
```
```  1314   using mult_right_mono [of a 0 b] by simp
```
```  1315
```
```  1316 text \<open>Legacy -- use @{thm [source] mult_nonpos_nonneg}.\<close>
```
```  1317 lemma mult_nonneg_nonpos2: "0 \<le> a \<Longrightarrow> b \<le> 0 \<Longrightarrow> b * a \<le> 0"
```
```  1318   by (drule mult_right_mono [of b 0]) auto
```
```  1319
```
```  1320 lemma split_mult_neg_le: "(0 \<le> a \<and> b \<le> 0) \<or> (a \<le> 0 \<and> 0 \<le> b) \<Longrightarrow> a * b \<le> 0"
```
```  1321   by (auto simp add: mult_nonneg_nonpos mult_nonneg_nonpos2)
```
```  1322
```
```  1323 end
```
```  1324
```
```  1325 class ordered_cancel_semiring = ordered_semiring + cancel_comm_monoid_add
```
```  1326 begin
```
```  1327
```
```  1328 subclass semiring_0_cancel ..
```
```  1329
```
```  1330 subclass ordered_semiring_0 ..
```
```  1331
```
```  1332 end
```
```  1333
```
```  1334 class linordered_semiring = ordered_semiring + linordered_cancel_ab_semigroup_add
```
```  1335 begin
```
```  1336
```
```  1337 subclass ordered_cancel_semiring ..
```
```  1338
```
```  1339 subclass ordered_cancel_comm_monoid_add ..
```
```  1340
```
```  1341 subclass ordered_ab_semigroup_monoid_add_imp_le ..
```
```  1342
```
```  1343 lemma mult_left_less_imp_less: "c * a < c * b \<Longrightarrow> 0 \<le> c \<Longrightarrow> a < b"
```
```  1344   by (force simp add: mult_left_mono not_le [symmetric])
```
```  1345
```
```  1346 lemma mult_right_less_imp_less: "a * c < b * c \<Longrightarrow> 0 \<le> c \<Longrightarrow> a < b"
```
```  1347   by (force simp add: mult_right_mono not_le [symmetric])
```
```  1348
```
```  1349 end
```
```  1350
```
```  1351 class linordered_semiring_1 = linordered_semiring + semiring_1
```
```  1352 begin
```
```  1353
```
```  1354 lemma convex_bound_le:
```
```  1355   assumes "x \<le> a" "y \<le> a" "0 \<le> u" "0 \<le> v" "u + v = 1"
```
```  1356   shows "u * x + v * y \<le> a"
```
```  1357 proof-
```
```  1358   from assms have "u * x + v * y \<le> u * a + v * a"
```
```  1359     by (simp add: add_mono mult_left_mono)
```
```  1360   with assms show ?thesis
```
```  1361     unfolding distrib_right[symmetric] by simp
```
```  1362 qed
```
```  1363
```
```  1364 end
```
```  1365
```
```  1366 class linordered_semiring_strict = semiring + comm_monoid_add + linordered_cancel_ab_semigroup_add +
```
```  1367   assumes mult_strict_left_mono: "a < b \<Longrightarrow> 0 < c \<Longrightarrow> c * a < c * b"
```
```  1368   assumes mult_strict_right_mono: "a < b \<Longrightarrow> 0 < c \<Longrightarrow> a * c < b * c"
```
```  1369 begin
```
```  1370
```
```  1371 subclass semiring_0_cancel ..
```
```  1372
```
```  1373 subclass linordered_semiring
```
```  1374 proof
```
```  1375   fix a b c :: 'a
```
```  1376   assume *: "a \<le> b" "0 \<le> c"
```
```  1377   then show "c * a \<le> c * b"
```
```  1378     unfolding le_less
```
```  1379     using mult_strict_left_mono by (cases "c = 0") auto
```
```  1380   from * show "a * c \<le> b * c"
```
```  1381     unfolding le_less
```
```  1382     using mult_strict_right_mono by (cases "c = 0") auto
```
```  1383 qed
```
```  1384
```
```  1385 lemma mult_left_le_imp_le: "c * a \<le> c * b \<Longrightarrow> 0 < c \<Longrightarrow> a \<le> b"
```
```  1386   by (auto simp add: mult_strict_left_mono _not_less [symmetric])
```
```  1387
```
```  1388 lemma mult_right_le_imp_le: "a * c \<le> b * c \<Longrightarrow> 0 < c \<Longrightarrow> a \<le> b"
```
```  1389   by (auto simp add: mult_strict_right_mono not_less [symmetric])
```
```  1390
```
```  1391 lemma mult_pos_pos[simp]: "0 < a \<Longrightarrow> 0 < b \<Longrightarrow> 0 < a * b"
```
```  1392   using mult_strict_left_mono [of 0 b a] by simp
```
```  1393
```
```  1394 lemma mult_pos_neg: "0 < a \<Longrightarrow> b < 0 \<Longrightarrow> a * b < 0"
```
```  1395   using mult_strict_left_mono [of b 0 a] by simp
```
```  1396
```
```  1397 lemma mult_neg_pos: "a < 0 \<Longrightarrow> 0 < b \<Longrightarrow> a * b < 0"
```
```  1398   using mult_strict_right_mono [of a 0 b] by simp
```
```  1399
```
```  1400 text \<open>Legacy -- use @{thm [source] mult_neg_pos}.\<close>
```
```  1401 lemma mult_pos_neg2: "0 < a \<Longrightarrow> b < 0 \<Longrightarrow> b * a < 0"
```
```  1402   by (drule mult_strict_right_mono [of b 0]) auto
```
```  1403
```
```  1404 lemma zero_less_mult_pos: "0 < a * b \<Longrightarrow> 0 < a \<Longrightarrow> 0 < b"
```
```  1405   apply (cases "b \<le> 0")
```
```  1406    apply (auto simp add: le_less not_less)
```
```  1407   apply (drule_tac mult_pos_neg [of a b])
```
```  1408    apply (auto dest: less_not_sym)
```
```  1409   done
```
```  1410
```
```  1411 lemma zero_less_mult_pos2: "0 < b * a \<Longrightarrow> 0 < a \<Longrightarrow> 0 < b"
```
```  1412   apply (cases "b \<le> 0")
```
```  1413    apply (auto simp add: le_less not_less)
```
```  1414   apply (drule_tac mult_pos_neg2 [of a b])
```
```  1415    apply (auto dest: less_not_sym)
```
```  1416   done
```
```  1417
```
```  1418 text \<open>Strict monotonicity in both arguments\<close>
```
```  1419 lemma mult_strict_mono:
```
```  1420   assumes "a < b" and "c < d" and "0 < b" and "0 \<le> c"
```
```  1421   shows "a * c < b * d"
```
```  1422   using assms
```
```  1423   apply (cases "c = 0")
```
```  1424    apply simp
```
```  1425   apply (erule mult_strict_right_mono [THEN less_trans])
```
```  1426    apply (auto simp add: le_less)
```
```  1427   apply (erule (1) mult_strict_left_mono)
```
```  1428   done
```
```  1429
```
```  1430 text \<open>This weaker variant has more natural premises\<close>
```
```  1431 lemma mult_strict_mono':
```
```  1432   assumes "a < b" and "c < d" and "0 \<le> a" and "0 \<le> c"
```
```  1433   shows "a * c < b * d"
```
```  1434   by (rule mult_strict_mono) (insert assms, auto)
```
```  1435
```
```  1436 lemma mult_less_le_imp_less:
```
```  1437   assumes "a < b" and "c \<le> d" and "0 \<le> a" and "0 < c"
```
```  1438   shows "a * c < b * d"
```
```  1439   using assms
```
```  1440   apply (subgoal_tac "a * c < b * c")
```
```  1441    apply (erule less_le_trans)
```
```  1442    apply (erule mult_left_mono)
```
```  1443    apply simp
```
```  1444   apply (erule (1) mult_strict_right_mono)
```
```  1445   done
```
```  1446
```
```  1447 lemma mult_le_less_imp_less:
```
```  1448   assumes "a \<le> b" and "c < d" and "0 < a" and "0 \<le> c"
```
```  1449   shows "a * c < b * d"
```
```  1450   using assms
```
```  1451   apply (subgoal_tac "a * c \<le> b * c")
```
```  1452    apply (erule le_less_trans)
```
```  1453    apply (erule mult_strict_left_mono)
```
```  1454    apply simp
```
```  1455   apply (erule (1) mult_right_mono)
```
```  1456   done
```
```  1457
```
```  1458 end
```
```  1459
```
```  1460 class linordered_semiring_1_strict = linordered_semiring_strict + semiring_1
```
```  1461 begin
```
```  1462
```
```  1463 subclass linordered_semiring_1 ..
```
```  1464
```
```  1465 lemma convex_bound_lt:
```
```  1466   assumes "x < a" "y < a" "0 \<le> u" "0 \<le> v" "u + v = 1"
```
```  1467   shows "u * x + v * y < a"
```
```  1468 proof -
```
```  1469   from assms have "u * x + v * y < u * a + v * a"
```
```  1470     by (cases "u = 0") (auto intro!: add_less_le_mono mult_strict_left_mono mult_left_mono)
```
```  1471   with assms show ?thesis
```
```  1472     unfolding distrib_right[symmetric] by simp
```
```  1473 qed
```
```  1474
```
```  1475 end
```
```  1476
```
```  1477 class ordered_comm_semiring = comm_semiring_0 + ordered_ab_semigroup_add +
```
```  1478   assumes comm_mult_left_mono: "a \<le> b \<Longrightarrow> 0 \<le> c \<Longrightarrow> c * a \<le> c * b"
```
```  1479 begin
```
```  1480
```
```  1481 subclass ordered_semiring
```
```  1482 proof
```
```  1483   fix a b c :: 'a
```
```  1484   assume "a \<le> b" "0 \<le> c"
```
```  1485   then show "c * a \<le> c * b" by (rule comm_mult_left_mono)
```
```  1486   then show "a * c \<le> b * c" by (simp only: mult.commute)
```
```  1487 qed
```
```  1488
```
```  1489 end
```
```  1490
```
```  1491 class ordered_cancel_comm_semiring = ordered_comm_semiring + cancel_comm_monoid_add
```
```  1492 begin
```
```  1493
```
```  1494 subclass comm_semiring_0_cancel ..
```
```  1495 subclass ordered_comm_semiring ..
```
```  1496 subclass ordered_cancel_semiring ..
```
```  1497
```
```  1498 end
```
```  1499
```
```  1500 class linordered_comm_semiring_strict = comm_semiring_0 + linordered_cancel_ab_semigroup_add +
```
```  1501   assumes comm_mult_strict_left_mono: "a < b \<Longrightarrow> 0 < c \<Longrightarrow> c * a < c * b"
```
```  1502 begin
```
```  1503
```
```  1504 subclass linordered_semiring_strict
```
```  1505 proof
```
```  1506   fix a b c :: 'a
```
```  1507   assume "a < b" "0 < c"
```
```  1508   then show "c * a < c * b"
```
```  1509     by (rule comm_mult_strict_left_mono)
```
```  1510   then show "a * c < b * c"
```
```  1511     by (simp only: mult.commute)
```
```  1512 qed
```
```  1513
```
```  1514 subclass ordered_cancel_comm_semiring
```
```  1515 proof
```
```  1516   fix a b c :: 'a
```
```  1517   assume "a \<le> b" "0 \<le> c"
```
```  1518   then show "c * a \<le> c * b"
```
```  1519     unfolding le_less
```
```  1520     using mult_strict_left_mono by (cases "c = 0") auto
```
```  1521 qed
```
```  1522
```
```  1523 end
```
```  1524
```
```  1525 class ordered_ring = ring + ordered_cancel_semiring
```
```  1526 begin
```
```  1527
```
```  1528 subclass ordered_ab_group_add ..
```
```  1529
```
```  1530 lemma less_add_iff1: "a * e + c < b * e + d \<longleftrightarrow> (a - b) * e + c < d"
```
```  1531   by (simp add: algebra_simps)
```
```  1532
```
```  1533 lemma less_add_iff2: "a * e + c < b * e + d \<longleftrightarrow> c < (b - a) * e + d"
```
```  1534   by (simp add: algebra_simps)
```
```  1535
```
```  1536 lemma le_add_iff1: "a * e + c \<le> b * e + d \<longleftrightarrow> (a - b) * e + c \<le> d"
```
```  1537   by (simp add: algebra_simps)
```
```  1538
```
```  1539 lemma le_add_iff2: "a * e + c \<le> b * e + d \<longleftrightarrow> c \<le> (b - a) * e + d"
```
```  1540   by (simp add: algebra_simps)
```
```  1541
```
```  1542 lemma mult_left_mono_neg: "b \<le> a \<Longrightarrow> c \<le> 0 \<Longrightarrow> c * a \<le> c * b"
```
```  1543   apply (drule mult_left_mono [of _ _ "- c"])
```
```  1544   apply simp_all
```
```  1545   done
```
```  1546
```
```  1547 lemma mult_right_mono_neg: "b \<le> a \<Longrightarrow> c \<le> 0 \<Longrightarrow> a * c \<le> b * c"
```
```  1548   apply (drule mult_right_mono [of _ _ "- c"])
```
```  1549   apply simp_all
```
```  1550   done
```
```  1551
```
```  1552 lemma mult_nonpos_nonpos: "a \<le> 0 \<Longrightarrow> b \<le> 0 \<Longrightarrow> 0 \<le> a * b"
```
```  1553   using mult_right_mono_neg [of a 0 b] by simp
```
```  1554
```
```  1555 lemma split_mult_pos_le: "(0 \<le> a \<and> 0 \<le> b) \<or> (a \<le> 0 \<and> b \<le> 0) \<Longrightarrow> 0 \<le> a * b"
```
```  1556   by (auto simp add: mult_nonpos_nonpos)
```
```  1557
```
```  1558 end
```
```  1559
```
```  1560 class linordered_ring = ring + linordered_semiring + linordered_ab_group_add + abs_if
```
```  1561 begin
```
```  1562
```
```  1563 subclass ordered_ring ..
```
```  1564
```
```  1565 subclass ordered_ab_group_add_abs
```
```  1566 proof
```
```  1567   fix a b
```
```  1568   show "\<bar>a + b\<bar> \<le> \<bar>a\<bar> + \<bar>b\<bar>"
```
```  1569     by (auto simp add: abs_if not_le not_less algebra_simps
```
```  1570         simp del: add.commute dest: add_neg_neg add_nonneg_nonneg)
```
```  1571 qed (auto simp: abs_if)
```
```  1572
```
```  1573 lemma zero_le_square [simp]: "0 \<le> a * a"
```
```  1574   using linear [of 0 a] by (auto simp add: mult_nonpos_nonpos)
```
```  1575
```
```  1576 lemma not_square_less_zero [simp]: "\<not> (a * a < 0)"
```
```  1577   by (simp add: not_less)
```
```  1578
```
```  1579 proposition abs_eq_iff: "\<bar>x\<bar> = \<bar>y\<bar> \<longleftrightarrow> x = y \<or> x = -y"
```
```  1580   by (auto simp add: abs_if split: if_split_asm)
```
```  1581
```
```  1582 lemma sum_squares_ge_zero: "0 \<le> x * x + y * y"
```
```  1583   by (intro add_nonneg_nonneg zero_le_square)
```
```  1584
```
```  1585 lemma not_sum_squares_lt_zero: "\<not> x * x + y * y < 0"
```
```  1586   by (simp add: not_less sum_squares_ge_zero)
```
```  1587
```
```  1588 end
```
```  1589
```
```  1590 class linordered_ring_strict = ring + linordered_semiring_strict
```
```  1591   + ordered_ab_group_add + abs_if
```
```  1592 begin
```
```  1593
```
```  1594 subclass linordered_ring ..
```
```  1595
```
```  1596 lemma mult_strict_left_mono_neg: "b < a \<Longrightarrow> c < 0 \<Longrightarrow> c * a < c * b"
```
```  1597   using mult_strict_left_mono [of b a "- c"] by simp
```
```  1598
```
```  1599 lemma mult_strict_right_mono_neg: "b < a \<Longrightarrow> c < 0 \<Longrightarrow> a * c < b * c"
```
```  1600   using mult_strict_right_mono [of b a "- c"] by simp
```
```  1601
```
```  1602 lemma mult_neg_neg: "a < 0 \<Longrightarrow> b < 0 \<Longrightarrow> 0 < a * b"
```
```  1603   using mult_strict_right_mono_neg [of a 0 b] by simp
```
```  1604
```
```  1605 subclass ring_no_zero_divisors
```
```  1606 proof
```
```  1607   fix a b
```
```  1608   assume "a \<noteq> 0"
```
```  1609   then have a: "a < 0 \<or> 0 < a" by (simp add: neq_iff)
```
```  1610   assume "b \<noteq> 0"
```
```  1611   then have b: "b < 0 \<or> 0 < b" by (simp add: neq_iff)
```
```  1612   have "a * b < 0 \<or> 0 < a * b"
```
```  1613   proof (cases "a < 0")
```
```  1614     case True
```
```  1615     show ?thesis
```
```  1616     proof (cases "b < 0")
```
```  1617       case True
```
```  1618       with \<open>a < 0\<close> show ?thesis by (auto dest: mult_neg_neg)
```
```  1619     next
```
```  1620       case False
```
```  1621       with b have "0 < b" by auto
```
```  1622       with \<open>a < 0\<close> show ?thesis by (auto dest: mult_strict_right_mono)
```
```  1623     qed
```
```  1624   next
```
```  1625     case False
```
```  1626     with a have "0 < a" by auto
```
```  1627     show ?thesis
```
```  1628     proof (cases "b < 0")
```
```  1629       case True
```
```  1630       with \<open>0 < a\<close> show ?thesis
```
```  1631         by (auto dest: mult_strict_right_mono_neg)
```
```  1632     next
```
```  1633       case False
```
```  1634       with b have "0 < b" by auto
```
```  1635       with \<open>0 < a\<close> show ?thesis by auto
```
```  1636     qed
```
```  1637   qed
```
```  1638   then show "a * b \<noteq> 0"
```
```  1639     by (simp add: neq_iff)
```
```  1640 qed
```
```  1641
```
```  1642 lemma zero_less_mult_iff: "0 < a * b \<longleftrightarrow> 0 < a \<and> 0 < b \<or> a < 0 \<and> b < 0"
```
```  1643   by (cases a 0 b 0 rule: linorder_cases[case_product linorder_cases])
```
```  1644      (auto simp add: mult_neg_neg not_less le_less dest: zero_less_mult_pos zero_less_mult_pos2)
```
```  1645
```
```  1646 lemma zero_le_mult_iff: "0 \<le> a * b \<longleftrightarrow> 0 \<le> a \<and> 0 \<le> b \<or> a \<le> 0 \<and> b \<le> 0"
```
```  1647   by (auto simp add: eq_commute [of 0] le_less not_less zero_less_mult_iff)
```
```  1648
```
```  1649 lemma mult_less_0_iff: "a * b < 0 \<longleftrightarrow> 0 < a \<and> b < 0 \<or> a < 0 \<and> 0 < b"
```
```  1650   using zero_less_mult_iff [of "- a" b] by auto
```
```  1651
```
```  1652 lemma mult_le_0_iff: "a * b \<le> 0 \<longleftrightarrow> 0 \<le> a \<and> b \<le> 0 \<or> a \<le> 0 \<and> 0 \<le> b"
```
```  1653   using zero_le_mult_iff [of "- a" b] by auto
```
```  1654
```
```  1655 text \<open>
```
```  1656   Cancellation laws for @{term "c * a < c * b"} and @{term "a * c < b * c"},
```
```  1657   also with the relations \<open>\<le>\<close> and equality.
```
```  1658 \<close>
```
```  1659
```
```  1660 text \<open>
```
```  1661   These ``disjunction'' versions produce two cases when the comparison is
```
```  1662   an assumption, but effectively four when the comparison is a goal.
```
```  1663 \<close>
```
```  1664
```
```  1665 lemma mult_less_cancel_right_disj: "a * c < b * c \<longleftrightarrow> 0 < c \<and> a < b \<or> c < 0 \<and>  b < a"
```
```  1666   apply (cases "c = 0")
```
```  1667    apply (auto simp add: neq_iff mult_strict_right_mono mult_strict_right_mono_neg)
```
```  1668      apply (auto simp add: not_less not_le [symmetric, of "a*c"] not_le [symmetric, of a])
```
```  1669      apply (erule_tac [!] notE)
```
```  1670      apply (auto simp add: less_imp_le mult_right_mono mult_right_mono_neg)
```
```  1671   done
```
```  1672
```
```  1673 lemma mult_less_cancel_left_disj: "c * a < c * b \<longleftrightarrow> 0 < c \<and> a < b \<or> c < 0 \<and>  b < a"
```
```  1674   apply (cases "c = 0")
```
```  1675    apply (auto simp add: neq_iff mult_strict_left_mono mult_strict_left_mono_neg)
```
```  1676      apply (auto simp add: not_less not_le [symmetric, of "c * a"] not_le [symmetric, of a])
```
```  1677      apply (erule_tac [!] notE)
```
```  1678      apply (auto simp add: less_imp_le mult_left_mono mult_left_mono_neg)
```
```  1679   done
```
```  1680
```
```  1681 text \<open>
```
```  1682   The ``conjunction of implication'' lemmas produce two cases when the
```
```  1683   comparison is a goal, but give four when the comparison is an assumption.
```
```  1684 \<close>
```
```  1685
```
```  1686 lemma mult_less_cancel_right: "a * c < b * c \<longleftrightarrow> (0 \<le> c \<longrightarrow> a < b) \<and> (c \<le> 0 \<longrightarrow> b < a)"
```
```  1687   using mult_less_cancel_right_disj [of a c b] by auto
```
```  1688
```
```  1689 lemma mult_less_cancel_left: "c * a < c * b \<longleftrightarrow> (0 \<le> c \<longrightarrow> a < b) \<and> (c \<le> 0 \<longrightarrow> b < a)"
```
```  1690   using mult_less_cancel_left_disj [of c a b] by auto
```
```  1691
```
```  1692 lemma mult_le_cancel_right: "a * c \<le> b * c \<longleftrightarrow> (0 < c \<longrightarrow> a \<le> b) \<and> (c < 0 \<longrightarrow> b \<le> a)"
```
```  1693   by (simp add: not_less [symmetric] mult_less_cancel_right_disj)
```
```  1694
```
```  1695 lemma mult_le_cancel_left: "c * a \<le> c * b \<longleftrightarrow> (0 < c \<longrightarrow> a \<le> b) \<and> (c < 0 \<longrightarrow> b \<le> a)"
```
```  1696   by (simp add: not_less [symmetric] mult_less_cancel_left_disj)
```
```  1697
```
```  1698 lemma mult_le_cancel_left_pos: "0 < c \<Longrightarrow> c * a \<le> c * b \<longleftrightarrow> a \<le> b"
```
```  1699   by (auto simp: mult_le_cancel_left)
```
```  1700
```
```  1701 lemma mult_le_cancel_left_neg: "c < 0 \<Longrightarrow> c * a \<le> c * b \<longleftrightarrow> b \<le> a"
```
```  1702   by (auto simp: mult_le_cancel_left)
```
```  1703
```
```  1704 lemma mult_less_cancel_left_pos: "0 < c \<Longrightarrow> c * a < c * b \<longleftrightarrow> a < b"
```
```  1705   by (auto simp: mult_less_cancel_left)
```
```  1706
```
```  1707 lemma mult_less_cancel_left_neg: "c < 0 \<Longrightarrow> c * a < c * b \<longleftrightarrow> b < a"
```
```  1708   by (auto simp: mult_less_cancel_left)
```
```  1709
```
```  1710 end
```
```  1711
```
```  1712 lemmas mult_sign_intros =
```
```  1713   mult_nonneg_nonneg mult_nonneg_nonpos
```
```  1714   mult_nonpos_nonneg mult_nonpos_nonpos
```
```  1715   mult_pos_pos mult_pos_neg
```
```  1716   mult_neg_pos mult_neg_neg
```
```  1717
```
```  1718 class ordered_comm_ring = comm_ring + ordered_comm_semiring
```
```  1719 begin
```
```  1720
```
```  1721 subclass ordered_ring ..
```
```  1722 subclass ordered_cancel_comm_semiring ..
```
```  1723
```
```  1724 end
```
```  1725
```
```  1726 class zero_less_one = order + zero + one +
```
```  1727   assumes zero_less_one [simp]: "0 < 1"
```
```  1728
```
```  1729 class linordered_nonzero_semiring = ordered_comm_semiring + monoid_mult + linorder + zero_less_one
```
```  1730 begin
```
```  1731
```
```  1732 subclass zero_neq_one
```
```  1733   by standard (insert zero_less_one, blast)
```
```  1734
```
```  1735 subclass comm_semiring_1
```
```  1736   by standard (rule mult_1_left)
```
```  1737
```
```  1738 lemma zero_le_one [simp]: "0 \<le> 1"
```
```  1739   by (rule zero_less_one [THEN less_imp_le])
```
```  1740
```
```  1741 lemma not_one_le_zero [simp]: "\<not> 1 \<le> 0"
```
```  1742   by (simp add: not_le)
```
```  1743
```
```  1744 lemma not_one_less_zero [simp]: "\<not> 1 < 0"
```
```  1745   by (simp add: not_less)
```
```  1746
```
```  1747 lemma mult_left_le: "c \<le> 1 \<Longrightarrow> 0 \<le> a \<Longrightarrow> a * c \<le> a"
```
```  1748   using mult_left_mono[of c 1 a] by simp
```
```  1749
```
```  1750 lemma mult_le_one: "a \<le> 1 \<Longrightarrow> 0 \<le> b \<Longrightarrow> b \<le> 1 \<Longrightarrow> a * b \<le> 1"
```
```  1751   using mult_mono[of a 1 b 1] by simp
```
```  1752
```
```  1753 lemma zero_less_two: "0 < 1 + 1"
```
```  1754   using add_pos_pos[OF zero_less_one zero_less_one] .
```
```  1755
```
```  1756 end
```
```  1757
```
```  1758 class linordered_semidom = semidom + linordered_comm_semiring_strict + zero_less_one +
```
```  1759   assumes le_add_diff_inverse2 [simp]: "b \<le> a \<Longrightarrow> a - b + b = a"
```
```  1760 begin
```
```  1761
```
```  1762 subclass linordered_nonzero_semiring ..
```
```  1763
```
```  1764 text \<open>Addition is the inverse of subtraction.\<close>
```
```  1765
```
```  1766 lemma le_add_diff_inverse [simp]: "b \<le> a \<Longrightarrow> b + (a - b) = a"
```
```  1767   by (frule le_add_diff_inverse2) (simp add: add.commute)
```
```  1768
```
```  1769 lemma add_diff_inverse: "\<not> a < b \<Longrightarrow> b + (a - b) = a"
```
```  1770   by simp
```
```  1771
```
```  1772 lemma add_le_imp_le_diff: "i + k \<le> n \<Longrightarrow> i \<le> n - k"
```
```  1773   apply (subst add_le_cancel_right [where c=k, symmetric])
```
```  1774   apply (frule le_add_diff_inverse2)
```
```  1775   apply (simp only: add.assoc [symmetric])
```
```  1776   using add_implies_diff
```
```  1777   apply fastforce
```
```  1778   done
```
```  1779
```
```  1780 lemma add_le_add_imp_diff_le:
```
```  1781   assumes 1: "i + k \<le> n"
```
```  1782     and 2: "n \<le> j + k"
```
```  1783   shows "i + k \<le> n \<Longrightarrow> n \<le> j + k \<Longrightarrow> n - k \<le> j"
```
```  1784 proof -
```
```  1785   have "n - (i + k) + (i + k) = n"
```
```  1786     using 1 by simp
```
```  1787   moreover have "n - k = n - k - i + i"
```
```  1788     using 1 by (simp add: add_le_imp_le_diff)
```
```  1789   ultimately show ?thesis
```
```  1790     using 2
```
```  1791     apply (simp add: add.assoc [symmetric])
```
```  1792     apply (rule add_le_imp_le_diff [of _ k "j + k", simplified add_diff_cancel_right'])
```
```  1793     apply (simp add: add.commute diff_diff_add)
```
```  1794     done
```
```  1795 qed
```
```  1796
```
```  1797 lemma less_1_mult: "1 < m \<Longrightarrow> 1 < n \<Longrightarrow> 1 < m * n"
```
```  1798   using mult_strict_mono [of 1 m 1 n] by (simp add: less_trans [OF zero_less_one])
```
```  1799
```
```  1800 end
```
```  1801
```
```  1802 class linordered_idom =
```
```  1803   comm_ring_1 + linordered_comm_semiring_strict + ordered_ab_group_add + abs_if + sgn_if
```
```  1804 begin
```
```  1805
```
```  1806 subclass linordered_semiring_1_strict ..
```
```  1807 subclass linordered_ring_strict ..
```
```  1808 subclass ordered_comm_ring ..
```
```  1809 subclass idom ..
```
```  1810
```
```  1811 subclass linordered_semidom
```
```  1812 proof
```
```  1813   have "0 \<le> 1 * 1" by (rule zero_le_square)
```
```  1814   then show "0 < 1" by (simp add: le_less)
```
```  1815   show "b \<le> a \<Longrightarrow> a - b + b = a" for a b by simp
```
```  1816 qed
```
```  1817
```
```  1818 lemma linorder_neqE_linordered_idom:
```
```  1819   assumes "x \<noteq> y"
```
```  1820   obtains "x < y" | "y < x"
```
```  1821   using assms by (rule neqE)
```
```  1822
```
```  1823 text \<open>These cancellation simp rules also produce two cases when the comparison is a goal.\<close>
```
```  1824
```
```  1825 lemma mult_le_cancel_right1: "c \<le> b * c \<longleftrightarrow> (0 < c \<longrightarrow> 1 \<le> b) \<and> (c < 0 \<longrightarrow> b \<le> 1)"
```
```  1826   using mult_le_cancel_right [of 1 c b] by simp
```
```  1827
```
```  1828 lemma mult_le_cancel_right2: "a * c \<le> c \<longleftrightarrow> (0 < c \<longrightarrow> a \<le> 1) \<and> (c < 0 \<longrightarrow> 1 \<le> a)"
```
```  1829   using mult_le_cancel_right [of a c 1] by simp
```
```  1830
```
```  1831 lemma mult_le_cancel_left1: "c \<le> c * b \<longleftrightarrow> (0 < c \<longrightarrow> 1 \<le> b) \<and> (c < 0 \<longrightarrow> b \<le> 1)"
```
```  1832   using mult_le_cancel_left [of c 1 b] by simp
```
```  1833
```
```  1834 lemma mult_le_cancel_left2: "c * a \<le> c \<longleftrightarrow> (0 < c \<longrightarrow> a \<le> 1) \<and> (c < 0 \<longrightarrow> 1 \<le> a)"
```
```  1835   using mult_le_cancel_left [of c a 1] by simp
```
```  1836
```
```  1837 lemma mult_less_cancel_right1: "c < b * c \<longleftrightarrow> (0 \<le> c \<longrightarrow> 1 < b) \<and> (c \<le> 0 \<longrightarrow> b < 1)"
```
```  1838   using mult_less_cancel_right [of 1 c b] by simp
```
```  1839
```
```  1840 lemma mult_less_cancel_right2: "a * c < c \<longleftrightarrow> (0 \<le> c \<longrightarrow> a < 1) \<and> (c \<le> 0 \<longrightarrow> 1 < a)"
```
```  1841   using mult_less_cancel_right [of a c 1] by simp
```
```  1842
```
```  1843 lemma mult_less_cancel_left1: "c < c * b \<longleftrightarrow> (0 \<le> c \<longrightarrow> 1 < b) \<and> (c \<le> 0 \<longrightarrow> b < 1)"
```
```  1844   using mult_less_cancel_left [of c 1 b] by simp
```
```  1845
```
```  1846 lemma mult_less_cancel_left2: "c * a < c \<longleftrightarrow> (0 \<le> c \<longrightarrow> a < 1) \<and> (c \<le> 0 \<longrightarrow> 1 < a)"
```
```  1847   using mult_less_cancel_left [of c a 1] by simp
```
```  1848
```
```  1849 lemma sgn_sgn [simp]: "sgn (sgn a) = sgn a"
```
```  1850   unfolding sgn_if by simp
```
```  1851
```
```  1852 lemma sgn_0_0: "sgn a = 0 \<longleftrightarrow> a = 0"
```
```  1853   unfolding sgn_if by simp
```
```  1854
```
```  1855 lemma sgn_1_pos: "sgn a = 1 \<longleftrightarrow> a > 0"
```
```  1856   unfolding sgn_if by simp
```
```  1857
```
```  1858 lemma sgn_1_neg: "sgn a = - 1 \<longleftrightarrow> a < 0"
```
```  1859   unfolding sgn_if by auto
```
```  1860
```
```  1861 lemma sgn_pos [simp]: "0 < a \<Longrightarrow> sgn a = 1"
```
```  1862   by (simp only: sgn_1_pos)
```
```  1863
```
```  1864 lemma sgn_neg [simp]: "a < 0 \<Longrightarrow> sgn a = - 1"
```
```  1865   by (simp only: sgn_1_neg)
```
```  1866
```
```  1867 lemma sgn_times: "sgn (a * b) = sgn a * sgn b"
```
```  1868   by (auto simp add: sgn_if zero_less_mult_iff)
```
```  1869
```
```  1870 lemma abs_sgn: "\<bar>k\<bar> = k * sgn k"
```
```  1871   unfolding sgn_if abs_if by auto
```
```  1872
```
```  1873 lemma sgn_greater [simp]: "0 < sgn a \<longleftrightarrow> 0 < a"
```
```  1874   unfolding sgn_if by auto
```
```  1875
```
```  1876 lemma sgn_less [simp]: "sgn a < 0 \<longleftrightarrow> a < 0"
```
```  1877   unfolding sgn_if by auto
```
```  1878
```
```  1879 lemma abs_sgn_eq: "\<bar>sgn a\<bar> = (if a = 0 then 0 else 1)"
```
```  1880   by (simp add: sgn_if)
```
```  1881
```
```  1882 lemma abs_dvd_iff [simp]: "\<bar>m\<bar> dvd k \<longleftrightarrow> m dvd k"
```
```  1883   by (simp add: abs_if)
```
```  1884
```
```  1885 lemma dvd_abs_iff [simp]: "m dvd \<bar>k\<bar> \<longleftrightarrow> m dvd k"
```
```  1886   by (simp add: abs_if)
```
```  1887
```
```  1888 lemma dvd_if_abs_eq: "\<bar>l\<bar> = \<bar>k\<bar> \<Longrightarrow> l dvd k"
```
```  1889   by (subst abs_dvd_iff [symmetric]) simp
```
```  1890
```
```  1891 text \<open>
```
```  1892   The following lemmas can be proven in more general structures, but
```
```  1893   are dangerous as simp rules in absence of @{thm neg_equal_zero},
```
```  1894   @{thm neg_less_pos}, @{thm neg_less_eq_nonneg}.
```
```  1895 \<close>
```
```  1896
```
```  1897 lemma equation_minus_iff_1 [simp, no_atp]: "1 = - a \<longleftrightarrow> a = - 1"
```
```  1898   by (fact equation_minus_iff)
```
```  1899
```
```  1900 lemma minus_equation_iff_1 [simp, no_atp]: "- a = 1 \<longleftrightarrow> a = - 1"
```
```  1901   by (subst minus_equation_iff, auto)
```
```  1902
```
```  1903 lemma le_minus_iff_1 [simp, no_atp]: "1 \<le> - b \<longleftrightarrow> b \<le> - 1"
```
```  1904   by (fact le_minus_iff)
```
```  1905
```
```  1906 lemma minus_le_iff_1 [simp, no_atp]: "- a \<le> 1 \<longleftrightarrow> - 1 \<le> a"
```
```  1907   by (fact minus_le_iff)
```
```  1908
```
```  1909 lemma less_minus_iff_1 [simp, no_atp]: "1 < - b \<longleftrightarrow> b < - 1"
```
```  1910   by (fact less_minus_iff)
```
```  1911
```
```  1912 lemma minus_less_iff_1 [simp, no_atp]: "- a < 1 \<longleftrightarrow> - 1 < a"
```
```  1913   by (fact minus_less_iff)
```
```  1914
```
```  1915 end
```
```  1916
```
```  1917 text \<open>Simprules for comparisons where common factors can be cancelled.\<close>
```
```  1918
```
```  1919 lemmas mult_compare_simps =
```
```  1920   mult_le_cancel_right mult_le_cancel_left
```
```  1921   mult_le_cancel_right1 mult_le_cancel_right2
```
```  1922   mult_le_cancel_left1 mult_le_cancel_left2
```
```  1923   mult_less_cancel_right mult_less_cancel_left
```
```  1924   mult_less_cancel_right1 mult_less_cancel_right2
```
```  1925   mult_less_cancel_left1 mult_less_cancel_left2
```
```  1926   mult_cancel_right mult_cancel_left
```
```  1927   mult_cancel_right1 mult_cancel_right2
```
```  1928   mult_cancel_left1 mult_cancel_left2
```
```  1929
```
```  1930
```
```  1931 text \<open>Reasoning about inequalities with division\<close>
```
```  1932
```
```  1933 context linordered_semidom
```
```  1934 begin
```
```  1935
```
```  1936 lemma less_add_one: "a < a + 1"
```
```  1937 proof -
```
```  1938   have "a + 0 < a + 1"
```
```  1939     by (blast intro: zero_less_one add_strict_left_mono)
```
```  1940   then show ?thesis by simp
```
```  1941 qed
```
```  1942
```
```  1943 end
```
```  1944
```
```  1945 context linordered_idom
```
```  1946 begin
```
```  1947
```
```  1948 lemma mult_right_le_one_le: "0 \<le> x \<Longrightarrow> 0 \<le> y \<Longrightarrow> y \<le> 1 \<Longrightarrow> x * y \<le> x"
```
```  1949   by (rule mult_left_le)
```
```  1950
```
```  1951 lemma mult_left_le_one_le: "0 \<le> x \<Longrightarrow> 0 \<le> y \<Longrightarrow> y \<le> 1 \<Longrightarrow> y * x \<le> x"
```
```  1952   by (auto simp add: mult_le_cancel_right2)
```
```  1953
```
```  1954 end
```
```  1955
```
```  1956 text \<open>Absolute Value\<close>
```
```  1957
```
```  1958 context linordered_idom
```
```  1959 begin
```
```  1960
```
```  1961 lemma mult_sgn_abs: "sgn x * \<bar>x\<bar> = x"
```
```  1962   unfolding abs_if sgn_if by auto
```
```  1963
```
```  1964 lemma abs_one [simp]: "\<bar>1\<bar> = 1"
```
```  1965   by (simp add: abs_if)
```
```  1966
```
```  1967 end
```
```  1968
```
```  1969 class ordered_ring_abs = ordered_ring + ordered_ab_group_add_abs +
```
```  1970   assumes abs_eq_mult:
```
```  1971     "(0 \<le> a \<or> a \<le> 0) \<and> (0 \<le> b \<or> b \<le> 0) \<Longrightarrow> \<bar>a * b\<bar> = \<bar>a\<bar> * \<bar>b\<bar>"
```
```  1972
```
```  1973 context linordered_idom
```
```  1974 begin
```
```  1975
```
```  1976 subclass ordered_ring_abs
```
```  1977   by standard (auto simp: abs_if not_less mult_less_0_iff)
```
```  1978
```
```  1979 lemma abs_mult: "\<bar>a * b\<bar> = \<bar>a\<bar> * \<bar>b\<bar>"
```
```  1980   by (rule abs_eq_mult) auto
```
```  1981
```
```  1982 lemma abs_mult_self [simp]: "\<bar>a\<bar> * \<bar>a\<bar> = a * a"
```
```  1983   by (simp add: abs_if)
```
```  1984
```
```  1985 lemma abs_mult_less:
```
```  1986   assumes ac: "\<bar>a\<bar> < c"
```
```  1987     and bd: "\<bar>b\<bar> < d"
```
```  1988   shows "\<bar>a\<bar> * \<bar>b\<bar> < c * d"
```
```  1989 proof -
```
```  1990   from ac have "0 < c"
```
```  1991     by (blast intro: le_less_trans abs_ge_zero)
```
```  1992   with bd show ?thesis by (simp add: ac mult_strict_mono)
```
```  1993 qed
```
```  1994
```
```  1995 lemma abs_less_iff: "\<bar>a\<bar> < b \<longleftrightarrow> a < b \<and> - a < b"
```
```  1996   by (simp add: less_le abs_le_iff) (auto simp add: abs_if)
```
```  1997
```
```  1998 lemma abs_mult_pos: "0 \<le> x \<Longrightarrow> \<bar>y\<bar> * x = \<bar>y * x\<bar>"
```
```  1999   by (simp add: abs_mult)
```
```  2000
```
```  2001 lemma abs_diff_less_iff: "\<bar>x - a\<bar> < r \<longleftrightarrow> a - r < x \<and> x < a + r"
```
```  2002   by (auto simp add: diff_less_eq ac_simps abs_less_iff)
```
```  2003
```
```  2004 lemma abs_diff_le_iff: "\<bar>x - a\<bar> \<le> r \<longleftrightarrow> a - r \<le> x \<and> x \<le> a + r"
```
```  2005   by (auto simp add: diff_le_eq ac_simps abs_le_iff)
```
```  2006
```
```  2007 lemma abs_add_one_gt_zero: "0 < 1 + \<bar>x\<bar>"
```
```  2008   by (auto simp: abs_if not_less intro: zero_less_one add_strict_increasing less_trans)
```
```  2009
```
```  2010 end
```
```  2011
```
```  2012 subsection \<open>Dioids\<close>
```
```  2013
```
```  2014 text \<open>
```
```  2015   Dioids are the alternative extensions of semirings, a semiring can
```
```  2016   either be a ring or a dioid but never both.
```
```  2017 \<close>
```
```  2018
```
```  2019 class dioid = semiring_1 + canonically_ordered_monoid_add
```
```  2020 begin
```
```  2021
```
```  2022 subclass ordered_semiring
```
```  2023   by standard (auto simp: le_iff_add distrib_left distrib_right)
```
```  2024
```
```  2025 end
```
```  2026
```
```  2027
```
```  2028 hide_fact (open) comm_mult_left_mono comm_mult_strict_left_mono distrib
```
```  2029
```
```  2030 code_identifier
```
```  2031   code_module Rings \<rightharpoonup> (SML) Arith and (OCaml) Arith and (Haskell) Arith
```
```  2032
```
```  2033 end
```