src/HOL/Divides.thy
 author wenzelm Tue Sep 01 22:32:58 2015 +0200 (2015-09-01) changeset 61076 bdc1e2f0a86a parent 60930 dd8ab7252ba2 child 61201 94efa2688ff6 permissions -rw-r--r--
eliminated \<Colon>;
```     1 (*  Title:      HOL/Divides.thy
```
```     2     Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
```
```     3     Copyright   1999  University of Cambridge
```
```     4 *)
```
```     5
```
```     6 section \<open>The division operators div and mod\<close>
```
```     7
```
```     8 theory Divides
```
```     9 imports Parity
```
```    10 begin
```
```    11
```
```    12 subsection \<open>Abstract division in commutative semirings.\<close>
```
```    13
```
```    14 class div = dvd + divide +
```
```    15   fixes mod :: "'a \<Rightarrow> 'a \<Rightarrow> 'a"  (infixl "mod" 70)
```
```    16
```
```    17 class semiring_div = semidom + div +
```
```    18   assumes mod_div_equality: "a div b * b + a mod b = a"
```
```    19     and div_by_0 [simp]: "a div 0 = 0"
```
```    20     and div_0 [simp]: "0 div a = 0"
```
```    21     and div_mult_self1 [simp]: "b \<noteq> 0 \<Longrightarrow> (a + c * b) div b = c + a div b"
```
```    22     and div_mult_mult1 [simp]: "c \<noteq> 0 \<Longrightarrow> (c * a) div (c * b) = a div b"
```
```    23 begin
```
```    24
```
```    25 subclass algebraic_semidom
```
```    26 proof
```
```    27   fix b a
```
```    28   assume "b \<noteq> 0"
```
```    29   then show "a * b div b = a"
```
```    30     using div_mult_self1 [of b 0 a] by (simp add: ac_simps)
```
```    31 qed simp
```
```    32
```
```    33 lemma div_by_1:
```
```    34   "a div 1 = a"
```
```    35   by (fact divide_1)
```
```    36
```
```    37 lemma div_mult_self1_is_id:
```
```    38   "b \<noteq> 0 \<Longrightarrow> b * a div b = a"
```
```    39   by (fact nonzero_mult_divide_cancel_left)
```
```    40
```
```    41 lemma div_mult_self2_is_id:
```
```    42   "b \<noteq> 0 \<Longrightarrow> a * b div b = a"
```
```    43   by (fact nonzero_mult_divide_cancel_right)
```
```    44
```
```    45 text \<open>@{const divide} and @{const mod}\<close>
```
```    46
```
```    47 lemma mod_div_equality2: "b * (a div b) + a mod b = a"
```
```    48   unfolding mult.commute [of b]
```
```    49   by (rule mod_div_equality)
```
```    50
```
```    51 lemma mod_div_equality': "a mod b + a div b * b = a"
```
```    52   using mod_div_equality [of a b]
```
```    53   by (simp only: ac_simps)
```
```    54
```
```    55 lemma div_mod_equality: "((a div b) * b + a mod b) + c = a + c"
```
```    56   by (simp add: mod_div_equality)
```
```    57
```
```    58 lemma div_mod_equality2: "(b * (a div b) + a mod b) + c = a + c"
```
```    59   by (simp add: mod_div_equality2)
```
```    60
```
```    61 lemma mod_by_0 [simp]: "a mod 0 = a"
```
```    62   using mod_div_equality [of a zero] by simp
```
```    63
```
```    64 lemma mod_0 [simp]: "0 mod a = 0"
```
```    65   using mod_div_equality [of zero a] div_0 by simp
```
```    66
```
```    67 lemma div_mult_self2 [simp]:
```
```    68   assumes "b \<noteq> 0"
```
```    69   shows "(a + b * c) div b = c + a div b"
```
```    70   using assms div_mult_self1 [of b a c] by (simp add: mult.commute)
```
```    71
```
```    72 lemma div_mult_self3 [simp]:
```
```    73   assumes "b \<noteq> 0"
```
```    74   shows "(c * b + a) div b = c + a div b"
```
```    75   using assms by (simp add: add.commute)
```
```    76
```
```    77 lemma div_mult_self4 [simp]:
```
```    78   assumes "b \<noteq> 0"
```
```    79   shows "(b * c + a) div b = c + a div b"
```
```    80   using assms by (simp add: add.commute)
```
```    81
```
```    82 lemma mod_mult_self1 [simp]: "(a + c * b) mod b = a mod b"
```
```    83 proof (cases "b = 0")
```
```    84   case True then show ?thesis by simp
```
```    85 next
```
```    86   case False
```
```    87   have "a + c * b = (a + c * b) div b * b + (a + c * b) mod b"
```
```    88     by (simp add: mod_div_equality)
```
```    89   also from False div_mult_self1 [of b a c] have
```
```    90     "\<dots> = (c + a div b) * b + (a + c * b) mod b"
```
```    91       by (simp add: algebra_simps)
```
```    92   finally have "a = a div b * b + (a + c * b) mod b"
```
```    93     by (simp add: add.commute [of a] add.assoc distrib_right)
```
```    94   then have "a div b * b + (a + c * b) mod b = a div b * b + a mod b"
```
```    95     by (simp add: mod_div_equality)
```
```    96   then show ?thesis by simp
```
```    97 qed
```
```    98
```
```    99 lemma mod_mult_self2 [simp]:
```
```   100   "(a + b * c) mod b = a mod b"
```
```   101   by (simp add: mult.commute [of b])
```
```   102
```
```   103 lemma mod_mult_self3 [simp]:
```
```   104   "(c * b + a) mod b = a mod b"
```
```   105   by (simp add: add.commute)
```
```   106
```
```   107 lemma mod_mult_self4 [simp]:
```
```   108   "(b * c + a) mod b = a mod b"
```
```   109   by (simp add: add.commute)
```
```   110
```
```   111 lemma mod_mult_self1_is_0 [simp]:
```
```   112   "b * a mod b = 0"
```
```   113   using mod_mult_self2 [of 0 b a] by simp
```
```   114
```
```   115 lemma mod_mult_self2_is_0 [simp]:
```
```   116   "a * b mod b = 0"
```
```   117   using mod_mult_self1 [of 0 a b] by simp
```
```   118
```
```   119 lemma mod_by_1 [simp]:
```
```   120   "a mod 1 = 0"
```
```   121 proof -
```
```   122   from mod_div_equality [of a one] div_by_1 have "a + a mod 1 = a" by simp
```
```   123   then have "a + a mod 1 = a + 0" by simp
```
```   124   then show ?thesis by (rule add_left_imp_eq)
```
```   125 qed
```
```   126
```
```   127 lemma mod_self [simp]:
```
```   128   "a mod a = 0"
```
```   129   using mod_mult_self2_is_0 [of 1] by simp
```
```   130
```
```   131 lemma div_add_self1 [simp]:
```
```   132   assumes "b \<noteq> 0"
```
```   133   shows "(b + a) div b = a div b + 1"
```
```   134   using assms div_mult_self1 [of b a 1] by (simp add: add.commute)
```
```   135
```
```   136 lemma div_add_self2 [simp]:
```
```   137   assumes "b \<noteq> 0"
```
```   138   shows "(a + b) div b = a div b + 1"
```
```   139   using assms div_add_self1 [of b a] by (simp add: add.commute)
```
```   140
```
```   141 lemma mod_add_self1 [simp]:
```
```   142   "(b + a) mod b = a mod b"
```
```   143   using mod_mult_self1 [of a 1 b] by (simp add: add.commute)
```
```   144
```
```   145 lemma mod_add_self2 [simp]:
```
```   146   "(a + b) mod b = a mod b"
```
```   147   using mod_mult_self1 [of a 1 b] by simp
```
```   148
```
```   149 lemma mod_div_decomp:
```
```   150   fixes a b
```
```   151   obtains q r where "q = a div b" and "r = a mod b"
```
```   152     and "a = q * b + r"
```
```   153 proof -
```
```   154   from mod_div_equality have "a = a div b * b + a mod b" by simp
```
```   155   moreover have "a div b = a div b" ..
```
```   156   moreover have "a mod b = a mod b" ..
```
```   157   note that ultimately show thesis by blast
```
```   158 qed
```
```   159
```
```   160 lemma dvd_imp_mod_0 [simp]:
```
```   161   assumes "a dvd b"
```
```   162   shows "b mod a = 0"
```
```   163 proof -
```
```   164   from assms obtain c where "b = a * c" ..
```
```   165   then have "b mod a = a * c mod a" by simp
```
```   166   then show "b mod a = 0" by simp
```
```   167 qed
```
```   168
```
```   169 lemma mod_eq_0_iff_dvd:
```
```   170   "a mod b = 0 \<longleftrightarrow> b dvd a"
```
```   171 proof
```
```   172   assume "b dvd a"
```
```   173   then show "a mod b = 0" by simp
```
```   174 next
```
```   175   assume "a mod b = 0"
```
```   176   with mod_div_equality [of a b] have "a div b * b = a" by simp
```
```   177   then have "a = b * (a div b)" by (simp add: ac_simps)
```
```   178   then show "b dvd a" ..
```
```   179 qed
```
```   180
```
```   181 lemma dvd_eq_mod_eq_0 [nitpick_unfold, code]:
```
```   182   "a dvd b \<longleftrightarrow> b mod a = 0"
```
```   183   by (simp add: mod_eq_0_iff_dvd)
```
```   184
```
```   185 lemma mod_div_trivial [simp]:
```
```   186   "a mod b div b = 0"
```
```   187 proof (cases "b = 0")
```
```   188   assume "b = 0"
```
```   189   thus ?thesis by simp
```
```   190 next
```
```   191   assume "b \<noteq> 0"
```
```   192   hence "a div b + a mod b div b = (a mod b + a div b * b) div b"
```
```   193     by (rule div_mult_self1 [symmetric])
```
```   194   also have "\<dots> = a div b"
```
```   195     by (simp only: mod_div_equality')
```
```   196   also have "\<dots> = a div b + 0"
```
```   197     by simp
```
```   198   finally show ?thesis
```
```   199     by (rule add_left_imp_eq)
```
```   200 qed
```
```   201
```
```   202 lemma mod_mod_trivial [simp]:
```
```   203   "a mod b mod b = a mod b"
```
```   204 proof -
```
```   205   have "a mod b mod b = (a mod b + a div b * b) mod b"
```
```   206     by (simp only: mod_mult_self1)
```
```   207   also have "\<dots> = a mod b"
```
```   208     by (simp only: mod_div_equality')
```
```   209   finally show ?thesis .
```
```   210 qed
```
```   211
```
```   212 lemma dvd_mod_imp_dvd:
```
```   213   assumes "k dvd m mod n" and "k dvd n"
```
```   214   shows "k dvd m"
```
```   215 proof -
```
```   216   from assms have "k dvd (m div n) * n + m mod n"
```
```   217     by (simp only: dvd_add dvd_mult)
```
```   218   then show ?thesis by (simp add: mod_div_equality)
```
```   219 qed
```
```   220
```
```   221 text \<open>Addition respects modular equivalence.\<close>
```
```   222
```
```   223 lemma mod_add_left_eq: -- \<open>FIXME reorient\<close>
```
```   224   "(a + b) mod c = (a mod c + b) mod c"
```
```   225 proof -
```
```   226   have "(a + b) mod c = (a div c * c + a mod c + b) mod c"
```
```   227     by (simp only: mod_div_equality)
```
```   228   also have "\<dots> = (a mod c + b + a div c * c) mod c"
```
```   229     by (simp only: ac_simps)
```
```   230   also have "\<dots> = (a mod c + b) mod c"
```
```   231     by (rule mod_mult_self1)
```
```   232   finally show ?thesis .
```
```   233 qed
```
```   234
```
```   235 lemma mod_add_right_eq: -- \<open>FIXME reorient\<close>
```
```   236   "(a + b) mod c = (a + b mod c) mod c"
```
```   237 proof -
```
```   238   have "(a + b) mod c = (a + (b div c * c + b mod c)) mod c"
```
```   239     by (simp only: mod_div_equality)
```
```   240   also have "\<dots> = (a + b mod c + b div c * c) mod c"
```
```   241     by (simp only: ac_simps)
```
```   242   also have "\<dots> = (a + b mod c) mod c"
```
```   243     by (rule mod_mult_self1)
```
```   244   finally show ?thesis .
```
```   245 qed
```
```   246
```
```   247 lemma mod_add_eq: -- \<open>FIXME reorient\<close>
```
```   248   "(a + b) mod c = (a mod c + b mod c) mod c"
```
```   249 by (rule trans [OF mod_add_left_eq mod_add_right_eq])
```
```   250
```
```   251 lemma mod_add_cong:
```
```   252   assumes "a mod c = a' mod c"
```
```   253   assumes "b mod c = b' mod c"
```
```   254   shows "(a + b) mod c = (a' + b') mod c"
```
```   255 proof -
```
```   256   have "(a mod c + b mod c) mod c = (a' mod c + b' mod c) mod c"
```
```   257     unfolding assms ..
```
```   258   thus ?thesis
```
```   259     by (simp only: mod_add_eq [symmetric])
```
```   260 qed
```
```   261
```
```   262 text \<open>Multiplication respects modular equivalence.\<close>
```
```   263
```
```   264 lemma mod_mult_left_eq: -- \<open>FIXME reorient\<close>
```
```   265   "(a * b) mod c = ((a mod c) * b) mod c"
```
```   266 proof -
```
```   267   have "(a * b) mod c = ((a div c * c + a mod c) * b) mod c"
```
```   268     by (simp only: mod_div_equality)
```
```   269   also have "\<dots> = (a mod c * b + a div c * b * c) mod c"
```
```   270     by (simp only: algebra_simps)
```
```   271   also have "\<dots> = (a mod c * b) mod c"
```
```   272     by (rule mod_mult_self1)
```
```   273   finally show ?thesis .
```
```   274 qed
```
```   275
```
```   276 lemma mod_mult_right_eq: -- \<open>FIXME reorient\<close>
```
```   277   "(a * b) mod c = (a * (b mod c)) mod c"
```
```   278 proof -
```
```   279   have "(a * b) mod c = (a * (b div c * c + b mod c)) mod c"
```
```   280     by (simp only: mod_div_equality)
```
```   281   also have "\<dots> = (a * (b mod c) + a * (b div c) * c) mod c"
```
```   282     by (simp only: algebra_simps)
```
```   283   also have "\<dots> = (a * (b mod c)) mod c"
```
```   284     by (rule mod_mult_self1)
```
```   285   finally show ?thesis .
```
```   286 qed
```
```   287
```
```   288 lemma mod_mult_eq: -- \<open>FIXME reorient\<close>
```
```   289   "(a * b) mod c = ((a mod c) * (b mod c)) mod c"
```
```   290 by (rule trans [OF mod_mult_left_eq mod_mult_right_eq])
```
```   291
```
```   292 lemma mod_mult_cong:
```
```   293   assumes "a mod c = a' mod c"
```
```   294   assumes "b mod c = b' mod c"
```
```   295   shows "(a * b) mod c = (a' * b') mod c"
```
```   296 proof -
```
```   297   have "(a mod c * (b mod c)) mod c = (a' mod c * (b' mod c)) mod c"
```
```   298     unfolding assms ..
```
```   299   thus ?thesis
```
```   300     by (simp only: mod_mult_eq [symmetric])
```
```   301 qed
```
```   302
```
```   303 text \<open>Exponentiation respects modular equivalence.\<close>
```
```   304
```
```   305 lemma power_mod: "(a mod b) ^ n mod b = a ^ n mod b"
```
```   306 apply (induct n, simp_all)
```
```   307 apply (rule mod_mult_right_eq [THEN trans])
```
```   308 apply (simp (no_asm_simp))
```
```   309 apply (rule mod_mult_eq [symmetric])
```
```   310 done
```
```   311
```
```   312 lemma mod_mod_cancel:
```
```   313   assumes "c dvd b"
```
```   314   shows "a mod b mod c = a mod c"
```
```   315 proof -
```
```   316   from \<open>c dvd b\<close> obtain k where "b = c * k"
```
```   317     by (rule dvdE)
```
```   318   have "a mod b mod c = a mod (c * k) mod c"
```
```   319     by (simp only: \<open>b = c * k\<close>)
```
```   320   also have "\<dots> = (a mod (c * k) + a div (c * k) * k * c) mod c"
```
```   321     by (simp only: mod_mult_self1)
```
```   322   also have "\<dots> = (a div (c * k) * (c * k) + a mod (c * k)) mod c"
```
```   323     by (simp only: ac_simps)
```
```   324   also have "\<dots> = a mod c"
```
```   325     by (simp only: mod_div_equality)
```
```   326   finally show ?thesis .
```
```   327 qed
```
```   328
```
```   329 lemma div_mult_mult2 [simp]:
```
```   330   "c \<noteq> 0 \<Longrightarrow> (a * c) div (b * c) = a div b"
```
```   331   by (drule div_mult_mult1) (simp add: mult.commute)
```
```   332
```
```   333 lemma div_mult_mult1_if [simp]:
```
```   334   "(c * a) div (c * b) = (if c = 0 then 0 else a div b)"
```
```   335   by simp_all
```
```   336
```
```   337 lemma mod_mult_mult1:
```
```   338   "(c * a) mod (c * b) = c * (a mod b)"
```
```   339 proof (cases "c = 0")
```
```   340   case True then show ?thesis by simp
```
```   341 next
```
```   342   case False
```
```   343   from mod_div_equality
```
```   344   have "((c * a) div (c * b)) * (c * b) + (c * a) mod (c * b) = c * a" .
```
```   345   with False have "c * ((a div b) * b + a mod b) + (c * a) mod (c * b)
```
```   346     = c * a + c * (a mod b)" by (simp add: algebra_simps)
```
```   347   with mod_div_equality show ?thesis by simp
```
```   348 qed
```
```   349
```
```   350 lemma mod_mult_mult2:
```
```   351   "(a * c) mod (b * c) = (a mod b) * c"
```
```   352   using mod_mult_mult1 [of c a b] by (simp add: mult.commute)
```
```   353
```
```   354 lemma mult_mod_left: "(a mod b) * c = (a * c) mod (b * c)"
```
```   355   by (fact mod_mult_mult2 [symmetric])
```
```   356
```
```   357 lemma mult_mod_right: "c * (a mod b) = (c * a) mod (c * b)"
```
```   358   by (fact mod_mult_mult1 [symmetric])
```
```   359
```
```   360 lemma dvd_mod: "k dvd m \<Longrightarrow> k dvd n \<Longrightarrow> k dvd (m mod n)"
```
```   361   unfolding dvd_def by (auto simp add: mod_mult_mult1)
```
```   362
```
```   363 lemma dvd_mod_iff: "k dvd n \<Longrightarrow> k dvd (m mod n) \<longleftrightarrow> k dvd m"
```
```   364 by (blast intro: dvd_mod_imp_dvd dvd_mod)
```
```   365
```
```   366 end
```
```   367
```
```   368 class ring_div = comm_ring_1 + semiring_div
```
```   369 begin
```
```   370
```
```   371 subclass idom_divide ..
```
```   372
```
```   373 text \<open>Negation respects modular equivalence.\<close>
```
```   374
```
```   375 lemma mod_minus_eq: "(- a) mod b = (- (a mod b)) mod b"
```
```   376 proof -
```
```   377   have "(- a) mod b = (- (a div b * b + a mod b)) mod b"
```
```   378     by (simp only: mod_div_equality)
```
```   379   also have "\<dots> = (- (a mod b) + - (a div b) * b) mod b"
```
```   380     by (simp add: ac_simps)
```
```   381   also have "\<dots> = (- (a mod b)) mod b"
```
```   382     by (rule mod_mult_self1)
```
```   383   finally show ?thesis .
```
```   384 qed
```
```   385
```
```   386 lemma mod_minus_cong:
```
```   387   assumes "a mod b = a' mod b"
```
```   388   shows "(- a) mod b = (- a') mod b"
```
```   389 proof -
```
```   390   have "(- (a mod b)) mod b = (- (a' mod b)) mod b"
```
```   391     unfolding assms ..
```
```   392   thus ?thesis
```
```   393     by (simp only: mod_minus_eq [symmetric])
```
```   394 qed
```
```   395
```
```   396 text \<open>Subtraction respects modular equivalence.\<close>
```
```   397
```
```   398 lemma mod_diff_left_eq:
```
```   399   "(a - b) mod c = (a mod c - b) mod c"
```
```   400   using mod_add_cong [of a c "a mod c" "- b" "- b"] by simp
```
```   401
```
```   402 lemma mod_diff_right_eq:
```
```   403   "(a - b) mod c = (a - b mod c) mod c"
```
```   404   using mod_add_cong [of a c a "- b" "- (b mod c)"] mod_minus_cong [of "b mod c" c b] by simp
```
```   405
```
```   406 lemma mod_diff_eq:
```
```   407   "(a - b) mod c = (a mod c - b mod c) mod c"
```
```   408   using mod_add_cong [of a c "a mod c" "- b" "- (b mod c)"] mod_minus_cong [of "b mod c" c b] by simp
```
```   409
```
```   410 lemma mod_diff_cong:
```
```   411   assumes "a mod c = a' mod c"
```
```   412   assumes "b mod c = b' mod c"
```
```   413   shows "(a - b) mod c = (a' - b') mod c"
```
```   414   using assms mod_add_cong [of a c a' "- b" "- b'"] mod_minus_cong [of b c "b'"] by simp
```
```   415
```
```   416 lemma dvd_neg_div: "y dvd x \<Longrightarrow> -x div y = - (x div y)"
```
```   417 apply (case_tac "y = 0") apply simp
```
```   418 apply (auto simp add: dvd_def)
```
```   419 apply (subgoal_tac "-(y * k) = y * - k")
```
```   420  apply (simp only:)
```
```   421  apply (erule div_mult_self1_is_id)
```
```   422 apply simp
```
```   423 done
```
```   424
```
```   425 lemma dvd_div_neg: "y dvd x \<Longrightarrow> x div -y = - (x div y)"
```
```   426 apply (case_tac "y = 0") apply simp
```
```   427 apply (auto simp add: dvd_def)
```
```   428 apply (subgoal_tac "y * k = -y * -k")
```
```   429  apply (erule ssubst, rule div_mult_self1_is_id)
```
```   430  apply simp
```
```   431 apply simp
```
```   432 done
```
```   433
```
```   434 lemma div_diff [simp]:
```
```   435   "z dvd x \<Longrightarrow> z dvd y \<Longrightarrow> (x - y) div z = x div z - y div z"
```
```   436   using div_add [of _ _ "- y"] by (simp add: dvd_neg_div)
```
```   437
```
```   438 lemma div_minus_minus [simp]: "(-a) div (-b) = a div b"
```
```   439   using div_mult_mult1 [of "- 1" a b]
```
```   440   unfolding neg_equal_0_iff_equal by simp
```
```   441
```
```   442 lemma mod_minus_minus [simp]: "(-a) mod (-b) = - (a mod b)"
```
```   443   using mod_mult_mult1 [of "- 1" a b] by simp
```
```   444
```
```   445 lemma div_minus_right: "a div (-b) = (-a) div b"
```
```   446   using div_minus_minus [of "-a" b] by simp
```
```   447
```
```   448 lemma mod_minus_right: "a mod (-b) = - ((-a) mod b)"
```
```   449   using mod_minus_minus [of "-a" b] by simp
```
```   450
```
```   451 lemma div_minus1_right [simp]: "a div (-1) = -a"
```
```   452   using div_minus_right [of a 1] by simp
```
```   453
```
```   454 lemma mod_minus1_right [simp]: "a mod (-1) = 0"
```
```   455   using mod_minus_right [of a 1] by simp
```
```   456
```
```   457 lemma minus_mod_self2 [simp]:
```
```   458   "(a - b) mod b = a mod b"
```
```   459   by (simp add: mod_diff_right_eq)
```
```   460
```
```   461 lemma minus_mod_self1 [simp]:
```
```   462   "(b - a) mod b = - a mod b"
```
```   463   using mod_add_self2 [of "- a" b] by simp
```
```   464
```
```   465 end
```
```   466
```
```   467
```
```   468 subsubsection \<open>Parity and division\<close>
```
```   469
```
```   470 class semiring_div_parity = semiring_div + comm_semiring_1_cancel + numeral +
```
```   471   assumes parity: "a mod 2 = 0 \<or> a mod 2 = 1"
```
```   472   assumes one_mod_two_eq_one [simp]: "1 mod 2 = 1"
```
```   473   assumes zero_not_eq_two: "0 \<noteq> 2"
```
```   474 begin
```
```   475
```
```   476 lemma parity_cases [case_names even odd]:
```
```   477   assumes "a mod 2 = 0 \<Longrightarrow> P"
```
```   478   assumes "a mod 2 = 1 \<Longrightarrow> P"
```
```   479   shows P
```
```   480   using assms parity by blast
```
```   481
```
```   482 lemma one_div_two_eq_zero [simp]:
```
```   483   "1 div 2 = 0"
```
```   484 proof (cases "2 = 0")
```
```   485   case True then show ?thesis by simp
```
```   486 next
```
```   487   case False
```
```   488   from mod_div_equality have "1 div 2 * 2 + 1 mod 2 = 1" .
```
```   489   with one_mod_two_eq_one have "1 div 2 * 2 + 1 = 1" by simp
```
```   490   then have "1 div 2 * 2 = 0" by (simp add: ac_simps add_left_imp_eq del: mult_eq_0_iff)
```
```   491   then have "1 div 2 = 0 \<or> 2 = 0" by simp
```
```   492   with False show ?thesis by auto
```
```   493 qed
```
```   494
```
```   495 lemma not_mod_2_eq_0_eq_1 [simp]:
```
```   496   "a mod 2 \<noteq> 0 \<longleftrightarrow> a mod 2 = 1"
```
```   497   by (cases a rule: parity_cases) simp_all
```
```   498
```
```   499 lemma not_mod_2_eq_1_eq_0 [simp]:
```
```   500   "a mod 2 \<noteq> 1 \<longleftrightarrow> a mod 2 = 0"
```
```   501   by (cases a rule: parity_cases) simp_all
```
```   502
```
```   503 subclass semiring_parity
```
```   504 proof (unfold_locales, unfold dvd_eq_mod_eq_0 not_mod_2_eq_0_eq_1)
```
```   505   show "1 mod 2 = 1"
```
```   506     by (fact one_mod_two_eq_one)
```
```   507 next
```
```   508   fix a b
```
```   509   assume "a mod 2 = 1"
```
```   510   moreover assume "b mod 2 = 1"
```
```   511   ultimately show "(a + b) mod 2 = 0"
```
```   512     using mod_add_eq [of a b 2] by simp
```
```   513 next
```
```   514   fix a b
```
```   515   assume "(a * b) mod 2 = 0"
```
```   516   then have "(a mod 2) * (b mod 2) = 0"
```
```   517     by (cases "a mod 2 = 0") (simp_all add: mod_mult_eq [of a b 2])
```
```   518   then show "a mod 2 = 0 \<or> b mod 2 = 0"
```
```   519     by (rule divisors_zero)
```
```   520 next
```
```   521   fix a
```
```   522   assume "a mod 2 = 1"
```
```   523   then have "a = a div 2 * 2 + 1" using mod_div_equality [of a 2] by simp
```
```   524   then show "\<exists>b. a = b + 1" ..
```
```   525 qed
```
```   526
```
```   527 lemma even_iff_mod_2_eq_zero:
```
```   528   "even a \<longleftrightarrow> a mod 2 = 0"
```
```   529   by (fact dvd_eq_mod_eq_0)
```
```   530
```
```   531 lemma even_succ_div_two [simp]:
```
```   532   "even a \<Longrightarrow> (a + 1) div 2 = a div 2"
```
```   533   by (cases "a = 0") (auto elim!: evenE dest: mult_not_zero)
```
```   534
```
```   535 lemma odd_succ_div_two [simp]:
```
```   536   "odd a \<Longrightarrow> (a + 1) div 2 = a div 2 + 1"
```
```   537   by (auto elim!: oddE simp add: zero_not_eq_two [symmetric] add.assoc)
```
```   538
```
```   539 lemma even_two_times_div_two:
```
```   540   "even a \<Longrightarrow> 2 * (a div 2) = a"
```
```   541   by (fact dvd_mult_div_cancel)
```
```   542
```
```   543 lemma odd_two_times_div_two_succ [simp]:
```
```   544   "odd a \<Longrightarrow> 2 * (a div 2) + 1 = a"
```
```   545   using mod_div_equality2 [of 2 a] by (simp add: even_iff_mod_2_eq_zero)
```
```   546
```
```   547 end
```
```   548
```
```   549
```
```   550 subsection \<open>Generic numeral division with a pragmatic type class\<close>
```
```   551
```
```   552 text \<open>
```
```   553   The following type class contains everything necessary to formulate
```
```   554   a division algorithm in ring structures with numerals, restricted
```
```   555   to its positive segments.  This is its primary motiviation, and it
```
```   556   could surely be formulated using a more fine-grained, more algebraic
```
```   557   and less technical class hierarchy.
```
```   558 \<close>
```
```   559
```
```   560 class semiring_numeral_div = semiring_div + comm_semiring_1_cancel + linordered_semidom +
```
```   561   assumes div_less: "0 \<le> a \<Longrightarrow> a < b \<Longrightarrow> a div b = 0"
```
```   562     and mod_less: " 0 \<le> a \<Longrightarrow> a < b \<Longrightarrow> a mod b = a"
```
```   563     and div_positive: "0 < b \<Longrightarrow> b \<le> a \<Longrightarrow> a div b > 0"
```
```   564     and mod_less_eq_dividend: "0 \<le> a \<Longrightarrow> a mod b \<le> a"
```
```   565     and pos_mod_bound: "0 < b \<Longrightarrow> a mod b < b"
```
```   566     and pos_mod_sign: "0 < b \<Longrightarrow> 0 \<le> a mod b"
```
```   567     and mod_mult2_eq: "0 \<le> c \<Longrightarrow> a mod (b * c) = b * (a div b mod c) + a mod b"
```
```   568     and div_mult2_eq: "0 \<le> c \<Longrightarrow> a div (b * c) = a div b div c"
```
```   569   assumes discrete: "a < b \<longleftrightarrow> a + 1 \<le> b"
```
```   570 begin
```
```   571
```
```   572 lemma mult_div_cancel:
```
```   573   "b * (a div b) = a - a mod b"
```
```   574 proof -
```
```   575   have "b * (a div b) + a mod b = a"
```
```   576     using mod_div_equality [of a b] by (simp add: ac_simps)
```
```   577   then have "b * (a div b) + a mod b - a mod b = a - a mod b"
```
```   578     by simp
```
```   579   then show ?thesis
```
```   580     by simp
```
```   581 qed
```
```   582
```
```   583 subclass semiring_div_parity
```
```   584 proof
```
```   585   fix a
```
```   586   show "a mod 2 = 0 \<or> a mod 2 = 1"
```
```   587   proof (rule ccontr)
```
```   588     assume "\<not> (a mod 2 = 0 \<or> a mod 2 = 1)"
```
```   589     then have "a mod 2 \<noteq> 0" and "a mod 2 \<noteq> 1" by simp_all
```
```   590     have "0 < 2" by simp
```
```   591     with pos_mod_bound pos_mod_sign have "0 \<le> a mod 2" "a mod 2 < 2" by simp_all
```
```   592     with \<open>a mod 2 \<noteq> 0\<close> have "0 < a mod 2" by simp
```
```   593     with discrete have "1 \<le> a mod 2" by simp
```
```   594     with \<open>a mod 2 \<noteq> 1\<close> have "1 < a mod 2" by simp
```
```   595     with discrete have "2 \<le> a mod 2" by simp
```
```   596     with \<open>a mod 2 < 2\<close> show False by simp
```
```   597   qed
```
```   598 next
```
```   599   show "1 mod 2 = 1"
```
```   600     by (rule mod_less) simp_all
```
```   601 next
```
```   602   show "0 \<noteq> 2"
```
```   603     by simp
```
```   604 qed
```
```   605
```
```   606 lemma divmod_digit_1:
```
```   607   assumes "0 \<le> a" "0 < b" and "b \<le> a mod (2 * b)"
```
```   608   shows "2 * (a div (2 * b)) + 1 = a div b" (is "?P")
```
```   609     and "a mod (2 * b) - b = a mod b" (is "?Q")
```
```   610 proof -
```
```   611   from assms mod_less_eq_dividend [of a "2 * b"] have "b \<le> a"
```
```   612     by (auto intro: trans)
```
```   613   with \<open>0 < b\<close> have "0 < a div b" by (auto intro: div_positive)
```
```   614   then have [simp]: "1 \<le> a div b" by (simp add: discrete)
```
```   615   with \<open>0 < b\<close> have mod_less: "a mod b < b" by (simp add: pos_mod_bound)
```
```   616   def w \<equiv> "a div b mod 2" with parity have w_exhaust: "w = 0 \<or> w = 1" by auto
```
```   617   have mod_w: "a mod (2 * b) = a mod b + b * w"
```
```   618     by (simp add: w_def mod_mult2_eq ac_simps)
```
```   619   from assms w_exhaust have "w = 1"
```
```   620     by (auto simp add: mod_w) (insert mod_less, auto)
```
```   621   with mod_w have mod: "a mod (2 * b) = a mod b + b" by simp
```
```   622   have "2 * (a div (2 * b)) = a div b - w"
```
```   623     by (simp add: w_def div_mult2_eq mult_div_cancel ac_simps)
```
```   624   with \<open>w = 1\<close> have div: "2 * (a div (2 * b)) = a div b - 1" by simp
```
```   625   then show ?P and ?Q
```
```   626     by (simp_all add: div mod add_implies_diff [symmetric])
```
```   627 qed
```
```   628
```
```   629 lemma divmod_digit_0:
```
```   630   assumes "0 < b" and "a mod (2 * b) < b"
```
```   631   shows "2 * (a div (2 * b)) = a div b" (is "?P")
```
```   632     and "a mod (2 * b) = a mod b" (is "?Q")
```
```   633 proof -
```
```   634   def w \<equiv> "a div b mod 2" with parity have w_exhaust: "w = 0 \<or> w = 1" by auto
```
```   635   have mod_w: "a mod (2 * b) = a mod b + b * w"
```
```   636     by (simp add: w_def mod_mult2_eq ac_simps)
```
```   637   moreover have "b \<le> a mod b + b"
```
```   638   proof -
```
```   639     from \<open>0 < b\<close> pos_mod_sign have "0 \<le> a mod b" by blast
```
```   640     then have "0 + b \<le> a mod b + b" by (rule add_right_mono)
```
```   641     then show ?thesis by simp
```
```   642   qed
```
```   643   moreover note assms w_exhaust
```
```   644   ultimately have "w = 0" by auto
```
```   645   with mod_w have mod: "a mod (2 * b) = a mod b" by simp
```
```   646   have "2 * (a div (2 * b)) = a div b - w"
```
```   647     by (simp add: w_def div_mult2_eq mult_div_cancel ac_simps)
```
```   648   with \<open>w = 0\<close> have div: "2 * (a div (2 * b)) = a div b" by simp
```
```   649   then show ?P and ?Q
```
```   650     by (simp_all add: div mod)
```
```   651 qed
```
```   652
```
```   653 definition divmod :: "num \<Rightarrow> num \<Rightarrow> 'a \<times> 'a"
```
```   654 where
```
```   655   "divmod m n = (numeral m div numeral n, numeral m mod numeral n)"
```
```   656
```
```   657 lemma fst_divmod:
```
```   658   "fst (divmod m n) = numeral m div numeral n"
```
```   659   by (simp add: divmod_def)
```
```   660
```
```   661 lemma snd_divmod:
```
```   662   "snd (divmod m n) = numeral m mod numeral n"
```
```   663   by (simp add: divmod_def)
```
```   664
```
```   665 definition divmod_step :: "num \<Rightarrow> 'a \<times> 'a \<Rightarrow> 'a \<times> 'a"
```
```   666 where
```
```   667   "divmod_step l qr = (let (q, r) = qr
```
```   668     in if r \<ge> numeral l then (2 * q + 1, r - numeral l)
```
```   669     else (2 * q, r))"
```
```   670
```
```   671 text \<open>
```
```   672   This is a formulation of one step (referring to one digit position)
```
```   673   in school-method division: compare the dividend at the current
```
```   674   digit position with the remainder from previous division steps
```
```   675   and evaluate accordingly.
```
```   676 \<close>
```
```   677
```
```   678 lemma divmod_step_eq [code, simp]:
```
```   679   "divmod_step l (q, r) = (if numeral l \<le> r
```
```   680     then (2 * q + 1, r - numeral l) else (2 * q, r))"
```
```   681   by (simp add: divmod_step_def)
```
```   682
```
```   683 text \<open>
```
```   684   This is a formulation of school-method division.
```
```   685   If the divisor is smaller than the dividend, terminate.
```
```   686   If not, shift the dividend to the right until termination
```
```   687   occurs and then reiterate single division steps in the
```
```   688   opposite direction.
```
```   689 \<close>
```
```   690
```
```   691 lemma divmod_divmod_step:
```
```   692   "divmod m n = (if m < n then (0, numeral m)
```
```   693     else divmod_step n (divmod m (Num.Bit0 n)))"
```
```   694 proof (cases "m < n")
```
```   695   case True then have "numeral m < numeral n" by simp
```
```   696   then show ?thesis
```
```   697     by (simp add: prod_eq_iff div_less mod_less fst_divmod snd_divmod)
```
```   698 next
```
```   699   case False
```
```   700   have "divmod m n =
```
```   701     divmod_step n (numeral m div (2 * numeral n),
```
```   702       numeral m mod (2 * numeral n))"
```
```   703   proof (cases "numeral n \<le> numeral m mod (2 * numeral n)")
```
```   704     case True
```
```   705     with divmod_step_eq
```
```   706       have "divmod_step n (numeral m div (2 * numeral n), numeral m mod (2 * numeral n)) =
```
```   707         (2 * (numeral m div (2 * numeral n)) + 1, numeral m mod (2 * numeral n) - numeral n)"
```
```   708         by simp
```
```   709     moreover from True divmod_digit_1 [of "numeral m" "numeral n"]
```
```   710       have "2 * (numeral m div (2 * numeral n)) + 1 = numeral m div numeral n"
```
```   711       and "numeral m mod (2 * numeral n) - numeral n = numeral m mod numeral n"
```
```   712       by simp_all
```
```   713     ultimately show ?thesis by (simp only: divmod_def)
```
```   714   next
```
```   715     case False then have *: "numeral m mod (2 * numeral n) < numeral n"
```
```   716       by (simp add: not_le)
```
```   717     with divmod_step_eq
```
```   718       have "divmod_step n (numeral m div (2 * numeral n), numeral m mod (2 * numeral n)) =
```
```   719         (2 * (numeral m div (2 * numeral n)), numeral m mod (2 * numeral n))"
```
```   720         by auto
```
```   721     moreover from * divmod_digit_0 [of "numeral n" "numeral m"]
```
```   722       have "2 * (numeral m div (2 * numeral n)) = numeral m div numeral n"
```
```   723       and "numeral m mod (2 * numeral n) = numeral m mod numeral n"
```
```   724       by (simp_all only: zero_less_numeral)
```
```   725     ultimately show ?thesis by (simp only: divmod_def)
```
```   726   qed
```
```   727   then have "divmod m n =
```
```   728     divmod_step n (numeral m div numeral (Num.Bit0 n),
```
```   729       numeral m mod numeral (Num.Bit0 n))"
```
```   730     by (simp only: numeral.simps distrib mult_1)
```
```   731   then have "divmod m n = divmod_step n (divmod m (Num.Bit0 n))"
```
```   732     by (simp add: divmod_def)
```
```   733   with False show ?thesis by simp
```
```   734 qed
```
```   735
```
```   736 text \<open>The division rewrite proper â€“ first, trivial results involving @{text 1}\<close>
```
```   737
```
```   738 lemma divmod_trivial [simp, code]:
```
```   739   "divmod Num.One Num.One = (numeral Num.One, 0)"
```
```   740   "divmod (Num.Bit0 m) Num.One = (numeral (Num.Bit0 m), 0)"
```
```   741   "divmod (Num.Bit1 m) Num.One = (numeral (Num.Bit1 m), 0)"
```
```   742   "divmod num.One (num.Bit0 n) = (0, Numeral1)"
```
```   743   "divmod num.One (num.Bit1 n) = (0, Numeral1)"
```
```   744   using divmod_divmod_step [of "Num.One"] by (simp_all add: divmod_def)
```
```   745
```
```   746 text \<open>Division by an even number is a right-shift\<close>
```
```   747
```
```   748 lemma divmod_cancel [simp, code]:
```
```   749   "divmod (Num.Bit0 m) (Num.Bit0 n) = (case divmod m n of (q, r) \<Rightarrow> (q, 2 * r))" (is ?P)
```
```   750   "divmod (Num.Bit1 m) (Num.Bit0 n) = (case divmod m n of (q, r) \<Rightarrow> (q, 2 * r + 1))" (is ?Q)
```
```   751 proof -
```
```   752   have *: "\<And>q. numeral (Num.Bit0 q) = 2 * numeral q"
```
```   753     "\<And>q. numeral (Num.Bit1 q) = 2 * numeral q + 1"
```
```   754     by (simp_all only: numeral_mult numeral.simps distrib) simp_all
```
```   755   have "1 div 2 = 0" "1 mod 2 = 1" by (auto intro: div_less mod_less)
```
```   756   then show ?P and ?Q
```
```   757     by (simp_all add: fst_divmod snd_divmod prod_eq_iff split_def * [of m] * [of n] mod_mult_mult1
```
```   758       div_mult2_eq [of _ _ 2] mod_mult2_eq [of _ _ 2]
```
```   759       add.commute del: numeral_times_numeral)
```
```   760 qed
```
```   761
```
```   762 text \<open>The really hard work\<close>
```
```   763
```
```   764 lemma divmod_steps [simp, code]:
```
```   765   "divmod (num.Bit0 m) (num.Bit1 n) =
```
```   766       (if m \<le> n then (0, numeral (num.Bit0 m))
```
```   767        else divmod_step (num.Bit1 n)
```
```   768              (divmod (num.Bit0 m)
```
```   769                (num.Bit0 (num.Bit1 n))))"
```
```   770   "divmod (num.Bit1 m) (num.Bit1 n) =
```
```   771       (if m < n then (0, numeral (num.Bit1 m))
```
```   772        else divmod_step (num.Bit1 n)
```
```   773              (divmod (num.Bit1 m)
```
```   774                (num.Bit0 (num.Bit1 n))))"
```
```   775   by (simp_all add: divmod_divmod_step)
```
```   776
```
```   777 text \<open>Special case: divisibility\<close>
```
```   778
```
```   779 definition divides_aux :: "'a \<times> 'a \<Rightarrow> bool"
```
```   780 where
```
```   781   "divides_aux qr \<longleftrightarrow> snd qr = 0"
```
```   782
```
```   783 lemma divides_aux_eq [simp]:
```
```   784   "divides_aux (q, r) \<longleftrightarrow> r = 0"
```
```   785   by (simp add: divides_aux_def)
```
```   786
```
```   787 lemma dvd_numeral_simp [simp]:
```
```   788   "numeral m dvd numeral n \<longleftrightarrow> divides_aux (divmod n m)"
```
```   789   by (simp add: divmod_def mod_eq_0_iff_dvd)
```
```   790
```
```   791 text \<open>Generic computation of quotient and remainder\<close>
```
```   792
```
```   793 lemma numeral_div_numeral [simp]:
```
```   794   "numeral k div numeral l = fst (divmod k l)"
```
```   795   by (simp add: fst_divmod)
```
```   796
```
```   797 lemma numeral_mod_numeral [simp]:
```
```   798   "numeral k mod numeral l = snd (divmod k l)"
```
```   799   by (simp add: snd_divmod)
```
```   800
```
```   801 lemma one_div_numeral [simp]:
```
```   802   "1 div numeral n = fst (divmod num.One n)"
```
```   803   by (simp add: fst_divmod)
```
```   804
```
```   805 lemma one_mod_numeral [simp]:
```
```   806   "1 mod numeral n = snd (divmod num.One n)"
```
```   807   by (simp add: snd_divmod)
```
```   808
```
```   809 end
```
```   810
```
```   811
```
```   812 subsection \<open>Division on @{typ nat}\<close>
```
```   813
```
```   814 text \<open>
```
```   815   We define @{const divide} and @{const mod} on @{typ nat} by means
```
```   816   of a characteristic relation with two input arguments
```
```   817   @{term "m::nat"}, @{term "n::nat"} and two output arguments
```
```   818   @{term "q::nat"}(uotient) and @{term "r::nat"}(emainder).
```
```   819 \<close>
```
```   820
```
```   821 definition divmod_nat_rel :: "nat \<Rightarrow> nat \<Rightarrow> nat \<times> nat \<Rightarrow> bool" where
```
```   822   "divmod_nat_rel m n qr \<longleftrightarrow>
```
```   823     m = fst qr * n + snd qr \<and>
```
```   824       (if n = 0 then fst qr = 0 else if n > 0 then 0 \<le> snd qr \<and> snd qr < n else n < snd qr \<and> snd qr \<le> 0)"
```
```   825
```
```   826 text \<open>@{const divmod_nat_rel} is total:\<close>
```
```   827
```
```   828 lemma divmod_nat_rel_ex:
```
```   829   obtains q r where "divmod_nat_rel m n (q, r)"
```
```   830 proof (cases "n = 0")
```
```   831   case True  with that show thesis
```
```   832     by (auto simp add: divmod_nat_rel_def)
```
```   833 next
```
```   834   case False
```
```   835   have "\<exists>q r. m = q * n + r \<and> r < n"
```
```   836   proof (induct m)
```
```   837     case 0 with \<open>n \<noteq> 0\<close>
```
```   838     have "(0::nat) = 0 * n + 0 \<and> 0 < n" by simp
```
```   839     then show ?case by blast
```
```   840   next
```
```   841     case (Suc m) then obtain q' r'
```
```   842       where m: "m = q' * n + r'" and n: "r' < n" by auto
```
```   843     then show ?case proof (cases "Suc r' < n")
```
```   844       case True
```
```   845       from m n have "Suc m = q' * n + Suc r'" by simp
```
```   846       with True show ?thesis by blast
```
```   847     next
```
```   848       case False then have "n \<le> Suc r'" by auto
```
```   849       moreover from n have "Suc r' \<le> n" by auto
```
```   850       ultimately have "n = Suc r'" by auto
```
```   851       with m have "Suc m = Suc q' * n + 0" by simp
```
```   852       with \<open>n \<noteq> 0\<close> show ?thesis by blast
```
```   853     qed
```
```   854   qed
```
```   855   with that show thesis
```
```   856     using \<open>n \<noteq> 0\<close> by (auto simp add: divmod_nat_rel_def)
```
```   857 qed
```
```   858
```
```   859 text \<open>@{const divmod_nat_rel} is injective:\<close>
```
```   860
```
```   861 lemma divmod_nat_rel_unique:
```
```   862   assumes "divmod_nat_rel m n qr"
```
```   863     and "divmod_nat_rel m n qr'"
```
```   864   shows "qr = qr'"
```
```   865 proof (cases "n = 0")
```
```   866   case True with assms show ?thesis
```
```   867     by (cases qr, cases qr')
```
```   868       (simp add: divmod_nat_rel_def)
```
```   869 next
```
```   870   case False
```
```   871   have aux: "\<And>q r q' r'. q' * n + r' = q * n + r \<Longrightarrow> r < n \<Longrightarrow> q' \<le> (q::nat)"
```
```   872   apply (rule leI)
```
```   873   apply (subst less_iff_Suc_add)
```
```   874   apply (auto simp add: add_mult_distrib)
```
```   875   done
```
```   876   from \<open>n \<noteq> 0\<close> assms have *: "fst qr = fst qr'"
```
```   877     by (auto simp add: divmod_nat_rel_def intro: order_antisym dest: aux sym)
```
```   878   with assms have "snd qr = snd qr'"
```
```   879     by (simp add: divmod_nat_rel_def)
```
```   880   with * show ?thesis by (cases qr, cases qr') simp
```
```   881 qed
```
```   882
```
```   883 text \<open>
```
```   884   We instantiate divisibility on the natural numbers by
```
```   885   means of @{const divmod_nat_rel}:
```
```   886 \<close>
```
```   887
```
```   888 definition divmod_nat :: "nat \<Rightarrow> nat \<Rightarrow> nat \<times> nat" where
```
```   889   "divmod_nat m n = (THE qr. divmod_nat_rel m n qr)"
```
```   890
```
```   891 lemma divmod_nat_rel_divmod_nat:
```
```   892   "divmod_nat_rel m n (divmod_nat m n)"
```
```   893 proof -
```
```   894   from divmod_nat_rel_ex
```
```   895     obtain qr where rel: "divmod_nat_rel m n qr" .
```
```   896   then show ?thesis
```
```   897   by (auto simp add: divmod_nat_def intro: theI elim: divmod_nat_rel_unique)
```
```   898 qed
```
```   899
```
```   900 lemma divmod_nat_unique:
```
```   901   assumes "divmod_nat_rel m n qr"
```
```   902   shows "divmod_nat m n = qr"
```
```   903   using assms by (auto intro: divmod_nat_rel_unique divmod_nat_rel_divmod_nat)
```
```   904
```
```   905 instantiation nat :: semiring_div
```
```   906 begin
```
```   907
```
```   908 definition divide_nat where
```
```   909   div_nat_def: "m div n = fst (divmod_nat m n)"
```
```   910
```
```   911 definition mod_nat where
```
```   912   "m mod n = snd (divmod_nat m n)"
```
```   913
```
```   914 lemma fst_divmod_nat [simp]:
```
```   915   "fst (divmod_nat m n) = m div n"
```
```   916   by (simp add: div_nat_def)
```
```   917
```
```   918 lemma snd_divmod_nat [simp]:
```
```   919   "snd (divmod_nat m n) = m mod n"
```
```   920   by (simp add: mod_nat_def)
```
```   921
```
```   922 lemma divmod_nat_div_mod:
```
```   923   "divmod_nat m n = (m div n, m mod n)"
```
```   924   by (simp add: prod_eq_iff)
```
```   925
```
```   926 lemma div_nat_unique:
```
```   927   assumes "divmod_nat_rel m n (q, r)"
```
```   928   shows "m div n = q"
```
```   929   using assms by (auto dest!: divmod_nat_unique simp add: prod_eq_iff)
```
```   930
```
```   931 lemma mod_nat_unique:
```
```   932   assumes "divmod_nat_rel m n (q, r)"
```
```   933   shows "m mod n = r"
```
```   934   using assms by (auto dest!: divmod_nat_unique simp add: prod_eq_iff)
```
```   935
```
```   936 lemma divmod_nat_rel: "divmod_nat_rel m n (m div n, m mod n)"
```
```   937   using divmod_nat_rel_divmod_nat by (simp add: divmod_nat_div_mod)
```
```   938
```
```   939 lemma divmod_nat_zero: "divmod_nat m 0 = (0, m)"
```
```   940   by (simp add: divmod_nat_unique divmod_nat_rel_def)
```
```   941
```
```   942 lemma divmod_nat_zero_left: "divmod_nat 0 n = (0, 0)"
```
```   943   by (simp add: divmod_nat_unique divmod_nat_rel_def)
```
```   944
```
```   945 lemma divmod_nat_base: "m < n \<Longrightarrow> divmod_nat m n = (0, m)"
```
```   946   by (simp add: divmod_nat_unique divmod_nat_rel_def)
```
```   947
```
```   948 lemma divmod_nat_step:
```
```   949   assumes "0 < n" and "n \<le> m"
```
```   950   shows "divmod_nat m n = (Suc ((m - n) div n), (m - n) mod n)"
```
```   951 proof (rule divmod_nat_unique)
```
```   952   have "divmod_nat_rel (m - n) n ((m - n) div n, (m - n) mod n)"
```
```   953     by (rule divmod_nat_rel)
```
```   954   thus "divmod_nat_rel m n (Suc ((m - n) div n), (m - n) mod n)"
```
```   955     unfolding divmod_nat_rel_def using assms by auto
```
```   956 qed
```
```   957
```
```   958 text \<open>The ''recursion'' equations for @{const divide} and @{const mod}\<close>
```
```   959
```
```   960 lemma div_less [simp]:
```
```   961   fixes m n :: nat
```
```   962   assumes "m < n"
```
```   963   shows "m div n = 0"
```
```   964   using assms divmod_nat_base by (simp add: prod_eq_iff)
```
```   965
```
```   966 lemma le_div_geq:
```
```   967   fixes m n :: nat
```
```   968   assumes "0 < n" and "n \<le> m"
```
```   969   shows "m div n = Suc ((m - n) div n)"
```
```   970   using assms divmod_nat_step by (simp add: prod_eq_iff)
```
```   971
```
```   972 lemma mod_less [simp]:
```
```   973   fixes m n :: nat
```
```   974   assumes "m < n"
```
```   975   shows "m mod n = m"
```
```   976   using assms divmod_nat_base by (simp add: prod_eq_iff)
```
```   977
```
```   978 lemma le_mod_geq:
```
```   979   fixes m n :: nat
```
```   980   assumes "n \<le> m"
```
```   981   shows "m mod n = (m - n) mod n"
```
```   982   using assms divmod_nat_step by (cases "n = 0") (simp_all add: prod_eq_iff)
```
```   983
```
```   984 instance proof
```
```   985   fix m n :: nat
```
```   986   show "m div n * n + m mod n = m"
```
```   987     using divmod_nat_rel [of m n] by (simp add: divmod_nat_rel_def)
```
```   988 next
```
```   989   fix m n q :: nat
```
```   990   assume "n \<noteq> 0"
```
```   991   then show "(q + m * n) div n = m + q div n"
```
```   992     by (induct m) (simp_all add: le_div_geq)
```
```   993 next
```
```   994   fix m n q :: nat
```
```   995   assume "m \<noteq> 0"
```
```   996   hence "\<And>a b. divmod_nat_rel n q (a, b) \<Longrightarrow> divmod_nat_rel (m * n) (m * q) (a, m * b)"
```
```   997     unfolding divmod_nat_rel_def
```
```   998     by (auto split: split_if_asm, simp_all add: algebra_simps)
```
```   999   moreover from divmod_nat_rel have "divmod_nat_rel n q (n div q, n mod q)" .
```
```  1000   ultimately have "divmod_nat_rel (m * n) (m * q) (n div q, m * (n mod q))" .
```
```  1001   thus "(m * n) div (m * q) = n div q" by (rule div_nat_unique)
```
```  1002 next
```
```  1003   fix n :: nat show "n div 0 = 0"
```
```  1004     by (simp add: div_nat_def divmod_nat_zero)
```
```  1005 next
```
```  1006   fix n :: nat show "0 div n = 0"
```
```  1007     by (simp add: div_nat_def divmod_nat_zero_left)
```
```  1008 qed
```
```  1009
```
```  1010 end
```
```  1011
```
```  1012 instantiation nat :: normalization_semidom
```
```  1013 begin
```
```  1014
```
```  1015 definition normalize_nat
```
```  1016   where [simp]: "normalize = (id :: nat \<Rightarrow> nat)"
```
```  1017
```
```  1018 definition unit_factor_nat
```
```  1019   where "unit_factor n = (if n = 0 then 0 else 1 :: nat)"
```
```  1020
```
```  1021 lemma unit_factor_simps [simp]:
```
```  1022   "unit_factor 0 = (0::nat)"
```
```  1023   "unit_factor (Suc n) = 1"
```
```  1024   by (simp_all add: unit_factor_nat_def)
```
```  1025
```
```  1026 instance
```
```  1027   by standard (simp_all add: unit_factor_nat_def)
```
```  1028
```
```  1029 end
```
```  1030
```
```  1031 lemma divmod_nat_if [code]: "divmod_nat m n = (if n = 0 \<or> m < n then (0, m) else
```
```  1032   let (q, r) = divmod_nat (m - n) n in (Suc q, r))"
```
```  1033   by (simp add: prod_eq_iff case_prod_beta not_less le_div_geq le_mod_geq)
```
```  1034
```
```  1035 text \<open>Simproc for cancelling @{const divide} and @{const mod}\<close>
```
```  1036
```
```  1037 ML_file "~~/src/Provers/Arith/cancel_div_mod.ML"
```
```  1038
```
```  1039 ML \<open>
```
```  1040 structure Cancel_Div_Mod_Nat = Cancel_Div_Mod
```
```  1041 (
```
```  1042   val div_name = @{const_name divide};
```
```  1043   val mod_name = @{const_name mod};
```
```  1044   val mk_binop = HOLogic.mk_binop;
```
```  1045   val mk_plus = HOLogic.mk_binop @{const_name Groups.plus};
```
```  1046   val dest_plus = HOLogic.dest_bin @{const_name Groups.plus} HOLogic.natT;
```
```  1047   fun mk_sum [] = HOLogic.zero
```
```  1048     | mk_sum [t] = t
```
```  1049     | mk_sum (t :: ts) = mk_plus (t, mk_sum ts);
```
```  1050   fun dest_sum tm =
```
```  1051     if HOLogic.is_zero tm then []
```
```  1052     else
```
```  1053       (case try HOLogic.dest_Suc tm of
```
```  1054         SOME t => HOLogic.Suc_zero :: dest_sum t
```
```  1055       | NONE =>
```
```  1056           (case try dest_plus tm of
```
```  1057             SOME (t, u) => dest_sum t @ dest_sum u
```
```  1058           | NONE => [tm]));
```
```  1059
```
```  1060   val div_mod_eqs = map mk_meta_eq [@{thm div_mod_equality}, @{thm div_mod_equality2}];
```
```  1061
```
```  1062   val prove_eq_sums = Arith_Data.prove_conv2 all_tac (Arith_Data.simp_all_tac
```
```  1063     (@{thm add_0_left} :: @{thm add_0_right} :: @{thms ac_simps}))
```
```  1064 )
```
```  1065 \<close>
```
```  1066
```
```  1067 simproc_setup cancel_div_mod_nat ("(m::nat) + n") = \<open>K Cancel_Div_Mod_Nat.proc\<close>
```
```  1068
```
```  1069
```
```  1070 subsubsection \<open>Quotient\<close>
```
```  1071
```
```  1072 lemma div_geq: "0 < n \<Longrightarrow>  \<not> m < n \<Longrightarrow> m div n = Suc ((m - n) div n)"
```
```  1073 by (simp add: le_div_geq linorder_not_less)
```
```  1074
```
```  1075 lemma div_if: "0 < n \<Longrightarrow> m div n = (if m < n then 0 else Suc ((m - n) div n))"
```
```  1076 by (simp add: div_geq)
```
```  1077
```
```  1078 lemma div_mult_self_is_m [simp]: "0<n ==> (m*n) div n = (m::nat)"
```
```  1079 by simp
```
```  1080
```
```  1081 lemma div_mult_self1_is_m [simp]: "0<n ==> (n*m) div n = (m::nat)"
```
```  1082 by simp
```
```  1083
```
```  1084 lemma div_positive:
```
```  1085   fixes m n :: nat
```
```  1086   assumes "n > 0"
```
```  1087   assumes "m \<ge> n"
```
```  1088   shows "m div n > 0"
```
```  1089 proof -
```
```  1090   from \<open>m \<ge> n\<close> obtain q where "m = n + q"
```
```  1091     by (auto simp add: le_iff_add)
```
```  1092   with \<open>n > 0\<close> show ?thesis by simp
```
```  1093 qed
```
```  1094
```
```  1095 lemma div_eq_0_iff: "(a div b::nat) = 0 \<longleftrightarrow> a < b \<or> b = 0"
```
```  1096   by (metis div_less div_positive div_by_0 gr0I less_numeral_extra(3) not_less)
```
```  1097
```
```  1098 subsubsection \<open>Remainder\<close>
```
```  1099
```
```  1100 lemma mod_less_divisor [simp]:
```
```  1101   fixes m n :: nat
```
```  1102   assumes "n > 0"
```
```  1103   shows "m mod n < (n::nat)"
```
```  1104   using assms divmod_nat_rel [of m n] unfolding divmod_nat_rel_def by auto
```
```  1105
```
```  1106 lemma mod_Suc_le_divisor [simp]:
```
```  1107   "m mod Suc n \<le> n"
```
```  1108   using mod_less_divisor [of "Suc n" m] by arith
```
```  1109
```
```  1110 lemma mod_less_eq_dividend [simp]:
```
```  1111   fixes m n :: nat
```
```  1112   shows "m mod n \<le> m"
```
```  1113 proof (rule add_leD2)
```
```  1114   from mod_div_equality have "m div n * n + m mod n = m" .
```
```  1115   then show "m div n * n + m mod n \<le> m" by auto
```
```  1116 qed
```
```  1117
```
```  1118 lemma mod_geq: "\<not> m < (n::nat) \<Longrightarrow> m mod n = (m - n) mod n"
```
```  1119 by (simp add: le_mod_geq linorder_not_less)
```
```  1120
```
```  1121 lemma mod_if: "m mod (n::nat) = (if m < n then m else (m - n) mod n)"
```
```  1122 by (simp add: le_mod_geq)
```
```  1123
```
```  1124 lemma mod_1 [simp]: "m mod Suc 0 = 0"
```
```  1125 by (induct m) (simp_all add: mod_geq)
```
```  1126
```
```  1127 (* a simple rearrangement of mod_div_equality: *)
```
```  1128 lemma mult_div_cancel: "(n::nat) * (m div n) = m - (m mod n)"
```
```  1129   using mod_div_equality2 [of n m] by arith
```
```  1130
```
```  1131 lemma mod_le_divisor[simp]: "0 < n \<Longrightarrow> m mod n \<le> (n::nat)"
```
```  1132   apply (drule mod_less_divisor [where m = m])
```
```  1133   apply simp
```
```  1134   done
```
```  1135
```
```  1136 subsubsection \<open>Quotient and Remainder\<close>
```
```  1137
```
```  1138 lemma divmod_nat_rel_mult1_eq:
```
```  1139   "divmod_nat_rel b c (q, r)
```
```  1140    \<Longrightarrow> divmod_nat_rel (a * b) c (a * q + a * r div c, a * r mod c)"
```
```  1141 by (auto simp add: split_ifs divmod_nat_rel_def algebra_simps)
```
```  1142
```
```  1143 lemma div_mult1_eq:
```
```  1144   "(a * b) div c = a * (b div c) + a * (b mod c) div (c::nat)"
```
```  1145 by (blast intro: divmod_nat_rel_mult1_eq [THEN div_nat_unique] divmod_nat_rel)
```
```  1146
```
```  1147 lemma divmod_nat_rel_add1_eq:
```
```  1148   "divmod_nat_rel a c (aq, ar) \<Longrightarrow> divmod_nat_rel b c (bq, br)
```
```  1149    \<Longrightarrow> divmod_nat_rel (a + b) c (aq + bq + (ar + br) div c, (ar + br) mod c)"
```
```  1150 by (auto simp add: split_ifs divmod_nat_rel_def algebra_simps)
```
```  1151
```
```  1152 (*NOT suitable for rewriting: the RHS has an instance of the LHS*)
```
```  1153 lemma div_add1_eq:
```
```  1154   "(a+b) div (c::nat) = a div c + b div c + ((a mod c + b mod c) div c)"
```
```  1155 by (blast intro: divmod_nat_rel_add1_eq [THEN div_nat_unique] divmod_nat_rel)
```
```  1156
```
```  1157 lemma divmod_nat_rel_mult2_eq:
```
```  1158   assumes "divmod_nat_rel a b (q, r)"
```
```  1159   shows "divmod_nat_rel a (b * c) (q div c, b *(q mod c) + r)"
```
```  1160 proof -
```
```  1161   { assume "r < b" and "0 < c"
```
```  1162     then have "b * (q mod c) + r < b * c"
```
```  1163       apply (cut_tac m = q and n = c in mod_less_divisor)
```
```  1164       apply (drule_tac [2] m = "q mod c" in less_imp_Suc_add, auto)
```
```  1165       apply (erule_tac P = "%x. lhs < rhs x" for lhs rhs in ssubst)
```
```  1166       apply (simp add: add_mult_distrib2)
```
```  1167       done
```
```  1168     then have "r + b * (q mod c) < b * c"
```
```  1169       by (simp add: ac_simps)
```
```  1170   } with assms show ?thesis
```
```  1171     by (auto simp add: divmod_nat_rel_def algebra_simps add_mult_distrib2 [symmetric])
```
```  1172 qed
```
```  1173
```
```  1174 lemma div_mult2_eq: "a div (b * c) = (a div b) div (c::nat)"
```
```  1175 by (force simp add: divmod_nat_rel [THEN divmod_nat_rel_mult2_eq, THEN div_nat_unique])
```
```  1176
```
```  1177 lemma mod_mult2_eq: "a mod (b * c) = b * (a div b mod c) + a mod (b::nat)"
```
```  1178 by (auto simp add: mult.commute divmod_nat_rel [THEN divmod_nat_rel_mult2_eq, THEN mod_nat_unique])
```
```  1179
```
```  1180 instance nat :: semiring_numeral_div
```
```  1181   by intro_classes (auto intro: div_positive simp add: mult_div_cancel mod_mult2_eq div_mult2_eq)
```
```  1182
```
```  1183
```
```  1184 subsubsection \<open>Further Facts about Quotient and Remainder\<close>
```
```  1185
```
```  1186 lemma div_1 [simp]:
```
```  1187   "m div Suc 0 = m"
```
```  1188   using div_by_1 [of m] by simp
```
```  1189
```
```  1190 (* Monotonicity of div in first argument *)
```
```  1191 lemma div_le_mono [rule_format (no_asm)]:
```
```  1192     "\<forall>m::nat. m \<le> n --> (m div k) \<le> (n div k)"
```
```  1193 apply (case_tac "k=0", simp)
```
```  1194 apply (induct "n" rule: nat_less_induct, clarify)
```
```  1195 apply (case_tac "n<k")
```
```  1196 (* 1  case n<k *)
```
```  1197 apply simp
```
```  1198 (* 2  case n >= k *)
```
```  1199 apply (case_tac "m<k")
```
```  1200 (* 2.1  case m<k *)
```
```  1201 apply simp
```
```  1202 (* 2.2  case m>=k *)
```
```  1203 apply (simp add: div_geq diff_le_mono)
```
```  1204 done
```
```  1205
```
```  1206 (* Antimonotonicity of div in second argument *)
```
```  1207 lemma div_le_mono2: "!!m::nat. [| 0<m; m\<le>n |] ==> (k div n) \<le> (k div m)"
```
```  1208 apply (subgoal_tac "0<n")
```
```  1209  prefer 2 apply simp
```
```  1210 apply (induct_tac k rule: nat_less_induct)
```
```  1211 apply (rename_tac "k")
```
```  1212 apply (case_tac "k<n", simp)
```
```  1213 apply (subgoal_tac "~ (k<m) ")
```
```  1214  prefer 2 apply simp
```
```  1215 apply (simp add: div_geq)
```
```  1216 apply (subgoal_tac "(k-n) div n \<le> (k-m) div n")
```
```  1217  prefer 2
```
```  1218  apply (blast intro: div_le_mono diff_le_mono2)
```
```  1219 apply (rule le_trans, simp)
```
```  1220 apply (simp)
```
```  1221 done
```
```  1222
```
```  1223 lemma div_le_dividend [simp]: "m div n \<le> (m::nat)"
```
```  1224 apply (case_tac "n=0", simp)
```
```  1225 apply (subgoal_tac "m div n \<le> m div 1", simp)
```
```  1226 apply (rule div_le_mono2)
```
```  1227 apply (simp_all (no_asm_simp))
```
```  1228 done
```
```  1229
```
```  1230 (* Similar for "less than" *)
```
```  1231 lemma div_less_dividend [simp]:
```
```  1232   "\<lbrakk>(1::nat) < n; 0 < m\<rbrakk> \<Longrightarrow> m div n < m"
```
```  1233 apply (induct m rule: nat_less_induct)
```
```  1234 apply (rename_tac "m")
```
```  1235 apply (case_tac "m<n", simp)
```
```  1236 apply (subgoal_tac "0<n")
```
```  1237  prefer 2 apply simp
```
```  1238 apply (simp add: div_geq)
```
```  1239 apply (case_tac "n<m")
```
```  1240  apply (subgoal_tac "(m-n) div n < (m-n) ")
```
```  1241   apply (rule impI less_trans_Suc)+
```
```  1242 apply assumption
```
```  1243   apply (simp_all)
```
```  1244 done
```
```  1245
```
```  1246 text\<open>A fact for the mutilated chess board\<close>
```
```  1247 lemma mod_Suc: "Suc(m) mod n = (if Suc(m mod n) = n then 0 else Suc(m mod n))"
```
```  1248 apply (case_tac "n=0", simp)
```
```  1249 apply (induct "m" rule: nat_less_induct)
```
```  1250 apply (case_tac "Suc (na) <n")
```
```  1251 (* case Suc(na) < n *)
```
```  1252 apply (frule lessI [THEN less_trans], simp add: less_not_refl3)
```
```  1253 (* case n \<le> Suc(na) *)
```
```  1254 apply (simp add: linorder_not_less le_Suc_eq mod_geq)
```
```  1255 apply (auto simp add: Suc_diff_le le_mod_geq)
```
```  1256 done
```
```  1257
```
```  1258 lemma mod_eq_0_iff: "(m mod d = 0) = (\<exists>q::nat. m = d*q)"
```
```  1259 by (auto simp add: dvd_eq_mod_eq_0 [symmetric] dvd_def)
```
```  1260
```
```  1261 lemmas mod_eq_0D [dest!] = mod_eq_0_iff [THEN iffD1]
```
```  1262
```
```  1263 (*Loses information, namely we also have r<d provided d is nonzero*)
```
```  1264 lemma mod_eqD:
```
```  1265   fixes m d r q :: nat
```
```  1266   assumes "m mod d = r"
```
```  1267   shows "\<exists>q. m = r + q * d"
```
```  1268 proof -
```
```  1269   from mod_div_equality obtain q where "q * d + m mod d = m" by blast
```
```  1270   with assms have "m = r + q * d" by simp
```
```  1271   then show ?thesis ..
```
```  1272 qed
```
```  1273
```
```  1274 lemma split_div:
```
```  1275  "P(n div k :: nat) =
```
```  1276  ((k = 0 \<longrightarrow> P 0) \<and> (k \<noteq> 0 \<longrightarrow> (!i. !j<k. n = k*i + j \<longrightarrow> P i)))"
```
```  1277  (is "?P = ?Q" is "_ = (_ \<and> (_ \<longrightarrow> ?R))")
```
```  1278 proof
```
```  1279   assume P: ?P
```
```  1280   show ?Q
```
```  1281   proof (cases)
```
```  1282     assume "k = 0"
```
```  1283     with P show ?Q by simp
```
```  1284   next
```
```  1285     assume not0: "k \<noteq> 0"
```
```  1286     thus ?Q
```
```  1287     proof (simp, intro allI impI)
```
```  1288       fix i j
```
```  1289       assume n: "n = k*i + j" and j: "j < k"
```
```  1290       show "P i"
```
```  1291       proof (cases)
```
```  1292         assume "i = 0"
```
```  1293         with n j P show "P i" by simp
```
```  1294       next
```
```  1295         assume "i \<noteq> 0"
```
```  1296         with not0 n j P show "P i" by(simp add:ac_simps)
```
```  1297       qed
```
```  1298     qed
```
```  1299   qed
```
```  1300 next
```
```  1301   assume Q: ?Q
```
```  1302   show ?P
```
```  1303   proof (cases)
```
```  1304     assume "k = 0"
```
```  1305     with Q show ?P by simp
```
```  1306   next
```
```  1307     assume not0: "k \<noteq> 0"
```
```  1308     with Q have R: ?R by simp
```
```  1309     from not0 R[THEN spec,of "n div k",THEN spec, of "n mod k"]
```
```  1310     show ?P by simp
```
```  1311   qed
```
```  1312 qed
```
```  1313
```
```  1314 lemma split_div_lemma:
```
```  1315   assumes "0 < n"
```
```  1316   shows "n * q \<le> m \<and> m < n * Suc q \<longleftrightarrow> q = ((m::nat) div n)" (is "?lhs \<longleftrightarrow> ?rhs")
```
```  1317 proof
```
```  1318   assume ?rhs
```
```  1319   with mult_div_cancel have nq: "n * q = m - (m mod n)" by simp
```
```  1320   then have A: "n * q \<le> m" by simp
```
```  1321   have "n - (m mod n) > 0" using mod_less_divisor assms by auto
```
```  1322   then have "m < m + (n - (m mod n))" by simp
```
```  1323   then have "m < n + (m - (m mod n))" by simp
```
```  1324   with nq have "m < n + n * q" by simp
```
```  1325   then have B: "m < n * Suc q" by simp
```
```  1326   from A B show ?lhs ..
```
```  1327 next
```
```  1328   assume P: ?lhs
```
```  1329   then have "divmod_nat_rel m n (q, m - n * q)"
```
```  1330     unfolding divmod_nat_rel_def by (auto simp add: ac_simps)
```
```  1331   with divmod_nat_rel_unique divmod_nat_rel [of m n]
```
```  1332   have "(q, m - n * q) = (m div n, m mod n)" by auto
```
```  1333   then show ?rhs by simp
```
```  1334 qed
```
```  1335
```
```  1336 theorem split_div':
```
```  1337   "P ((m::nat) div n) = ((n = 0 \<and> P 0) \<or>
```
```  1338    (\<exists>q. (n * q \<le> m \<and> m < n * (Suc q)) \<and> P q))"
```
```  1339   apply (case_tac "0 < n")
```
```  1340   apply (simp only: add: split_div_lemma)
```
```  1341   apply simp_all
```
```  1342   done
```
```  1343
```
```  1344 lemma split_mod:
```
```  1345  "P(n mod k :: nat) =
```
```  1346  ((k = 0 \<longrightarrow> P n) \<and> (k \<noteq> 0 \<longrightarrow> (!i. !j<k. n = k*i + j \<longrightarrow> P j)))"
```
```  1347  (is "?P = ?Q" is "_ = (_ \<and> (_ \<longrightarrow> ?R))")
```
```  1348 proof
```
```  1349   assume P: ?P
```
```  1350   show ?Q
```
```  1351   proof (cases)
```
```  1352     assume "k = 0"
```
```  1353     with P show ?Q by simp
```
```  1354   next
```
```  1355     assume not0: "k \<noteq> 0"
```
```  1356     thus ?Q
```
```  1357     proof (simp, intro allI impI)
```
```  1358       fix i j
```
```  1359       assume "n = k*i + j" "j < k"
```
```  1360       thus "P j" using not0 P by (simp add: ac_simps)
```
```  1361     qed
```
```  1362   qed
```
```  1363 next
```
```  1364   assume Q: ?Q
```
```  1365   show ?P
```
```  1366   proof (cases)
```
```  1367     assume "k = 0"
```
```  1368     with Q show ?P by simp
```
```  1369   next
```
```  1370     assume not0: "k \<noteq> 0"
```
```  1371     with Q have R: ?R by simp
```
```  1372     from not0 R[THEN spec,of "n div k",THEN spec, of "n mod k"]
```
```  1373     show ?P by simp
```
```  1374   qed
```
```  1375 qed
```
```  1376
```
```  1377 theorem mod_div_equality' [nitpick_unfold]: "(m::nat) mod n = m - (m div n) * n"
```
```  1378   using mod_div_equality [of m n] by arith
```
```  1379
```
```  1380 lemma div_mod_equality': "(m::nat) div n * n = m - m mod n"
```
```  1381   using mod_div_equality [of m n] by arith
```
```  1382 (* FIXME: very similar to mult_div_cancel *)
```
```  1383
```
```  1384 lemma div_eq_dividend_iff: "a \<noteq> 0 \<Longrightarrow> (a :: nat) div b = a \<longleftrightarrow> b = 1"
```
```  1385   apply rule
```
```  1386   apply (cases "b = 0")
```
```  1387   apply simp_all
```
```  1388   apply (metis (full_types) One_nat_def Suc_lessI div_less_dividend less_not_refl3)
```
```  1389   done
```
```  1390
```
```  1391
```
```  1392 subsubsection \<open>An ``induction'' law for modulus arithmetic.\<close>
```
```  1393
```
```  1394 lemma mod_induct_0:
```
```  1395   assumes step: "\<forall>i<p. P i \<longrightarrow> P ((Suc i) mod p)"
```
```  1396   and base: "P i" and i: "i<p"
```
```  1397   shows "P 0"
```
```  1398 proof (rule ccontr)
```
```  1399   assume contra: "\<not>(P 0)"
```
```  1400   from i have p: "0<p" by simp
```
```  1401   have "\<forall>k. 0<k \<longrightarrow> \<not> P (p-k)" (is "\<forall>k. ?A k")
```
```  1402   proof
```
```  1403     fix k
```
```  1404     show "?A k"
```
```  1405     proof (induct k)
```
```  1406       show "?A 0" by simp  -- "by contradiction"
```
```  1407     next
```
```  1408       fix n
```
```  1409       assume ih: "?A n"
```
```  1410       show "?A (Suc n)"
```
```  1411       proof (clarsimp)
```
```  1412         assume y: "P (p - Suc n)"
```
```  1413         have n: "Suc n < p"
```
```  1414         proof (rule ccontr)
```
```  1415           assume "\<not>(Suc n < p)"
```
```  1416           hence "p - Suc n = 0"
```
```  1417             by simp
```
```  1418           with y contra show "False"
```
```  1419             by simp
```
```  1420         qed
```
```  1421         hence n2: "Suc (p - Suc n) = p-n" by arith
```
```  1422         from p have "p - Suc n < p" by arith
```
```  1423         with y step have z: "P ((Suc (p - Suc n)) mod p)"
```
```  1424           by blast
```
```  1425         show "False"
```
```  1426         proof (cases "n=0")
```
```  1427           case True
```
```  1428           with z n2 contra show ?thesis by simp
```
```  1429         next
```
```  1430           case False
```
```  1431           with p have "p-n < p" by arith
```
```  1432           with z n2 False ih show ?thesis by simp
```
```  1433         qed
```
```  1434       qed
```
```  1435     qed
```
```  1436   qed
```
```  1437   moreover
```
```  1438   from i obtain k where "0<k \<and> i+k=p"
```
```  1439     by (blast dest: less_imp_add_positive)
```
```  1440   hence "0<k \<and> i=p-k" by auto
```
```  1441   moreover
```
```  1442   note base
```
```  1443   ultimately
```
```  1444   show "False" by blast
```
```  1445 qed
```
```  1446
```
```  1447 lemma mod_induct:
```
```  1448   assumes step: "\<forall>i<p. P i \<longrightarrow> P ((Suc i) mod p)"
```
```  1449   and base: "P i" and i: "i<p" and j: "j<p"
```
```  1450   shows "P j"
```
```  1451 proof -
```
```  1452   have "\<forall>j<p. P j"
```
```  1453   proof
```
```  1454     fix j
```
```  1455     show "j<p \<longrightarrow> P j" (is "?A j")
```
```  1456     proof (induct j)
```
```  1457       from step base i show "?A 0"
```
```  1458         by (auto elim: mod_induct_0)
```
```  1459     next
```
```  1460       fix k
```
```  1461       assume ih: "?A k"
```
```  1462       show "?A (Suc k)"
```
```  1463       proof
```
```  1464         assume suc: "Suc k < p"
```
```  1465         hence k: "k<p" by simp
```
```  1466         with ih have "P k" ..
```
```  1467         with step k have "P (Suc k mod p)"
```
```  1468           by blast
```
```  1469         moreover
```
```  1470         from suc have "Suc k mod p = Suc k"
```
```  1471           by simp
```
```  1472         ultimately
```
```  1473         show "P (Suc k)" by simp
```
```  1474       qed
```
```  1475     qed
```
```  1476   qed
```
```  1477   with j show ?thesis by blast
```
```  1478 qed
```
```  1479
```
```  1480 lemma div2_Suc_Suc [simp]: "Suc (Suc m) div 2 = Suc (m div 2)"
```
```  1481   by (simp add: numeral_2_eq_2 le_div_geq)
```
```  1482
```
```  1483 lemma mod2_Suc_Suc [simp]: "Suc (Suc m) mod 2 = m mod 2"
```
```  1484   by (simp add: numeral_2_eq_2 le_mod_geq)
```
```  1485
```
```  1486 lemma add_self_div_2 [simp]: "(m + m) div 2 = (m::nat)"
```
```  1487 by (simp add: mult_2 [symmetric])
```
```  1488
```
```  1489 lemma mod2_gr_0 [simp]: "0 < (m::nat) mod 2 \<longleftrightarrow> m mod 2 = 1"
```
```  1490 proof -
```
```  1491   { fix n :: nat have  "(n::nat) < 2 \<Longrightarrow> n = 0 \<or> n = 1" by (cases n) simp_all }
```
```  1492   moreover have "m mod 2 < 2" by simp
```
```  1493   ultimately have "m mod 2 = 0 \<or> m mod 2 = 1" .
```
```  1494   then show ?thesis by auto
```
```  1495 qed
```
```  1496
```
```  1497 text\<open>These lemmas collapse some needless occurrences of Suc:
```
```  1498     at least three Sucs, since two and fewer are rewritten back to Suc again!
```
```  1499     We already have some rules to simplify operands smaller than 3.\<close>
```
```  1500
```
```  1501 lemma div_Suc_eq_div_add3 [simp]: "m div (Suc (Suc (Suc n))) = m div (3+n)"
```
```  1502 by (simp add: Suc3_eq_add_3)
```
```  1503
```
```  1504 lemma mod_Suc_eq_mod_add3 [simp]: "m mod (Suc (Suc (Suc n))) = m mod (3+n)"
```
```  1505 by (simp add: Suc3_eq_add_3)
```
```  1506
```
```  1507 lemma Suc_div_eq_add3_div: "(Suc (Suc (Suc m))) div n = (3+m) div n"
```
```  1508 by (simp add: Suc3_eq_add_3)
```
```  1509
```
```  1510 lemma Suc_mod_eq_add3_mod: "(Suc (Suc (Suc m))) mod n = (3+m) mod n"
```
```  1511 by (simp add: Suc3_eq_add_3)
```
```  1512
```
```  1513 lemmas Suc_div_eq_add3_div_numeral [simp] = Suc_div_eq_add3_div [of _ "numeral v"] for v
```
```  1514 lemmas Suc_mod_eq_add3_mod_numeral [simp] = Suc_mod_eq_add3_mod [of _ "numeral v"] for v
```
```  1515
```
```  1516 lemma Suc_times_mod_eq: "1<k ==> Suc (k * m) mod k = 1"
```
```  1517 apply (induct "m")
```
```  1518 apply (simp_all add: mod_Suc)
```
```  1519 done
```
```  1520
```
```  1521 declare Suc_times_mod_eq [of "numeral w", simp] for w
```
```  1522
```
```  1523 lemma mod_greater_zero_iff_not_dvd:
```
```  1524   fixes m n :: nat
```
```  1525   shows "m mod n > 0 \<longleftrightarrow> \<not> n dvd m"
```
```  1526   by (simp add: dvd_eq_mod_eq_0)
```
```  1527
```
```  1528 lemma Suc_div_le_mono [simp]: "n div k \<le> (Suc n) div k"
```
```  1529 by (simp add: div_le_mono)
```
```  1530
```
```  1531 lemma Suc_n_div_2_gt_zero [simp]: "(0::nat) < n ==> 0 < (n + 1) div 2"
```
```  1532 by (cases n) simp_all
```
```  1533
```
```  1534 lemma div_2_gt_zero [simp]: assumes A: "(1::nat) < n" shows "0 < n div 2"
```
```  1535 proof -
```
```  1536   from A have B: "0 < n - 1" and C: "n - 1 + 1 = n" by simp_all
```
```  1537   from Suc_n_div_2_gt_zero [OF B] C show ?thesis by simp
```
```  1538 qed
```
```  1539
```
```  1540 lemma mod_mult_self4 [simp]: "Suc (k*n + m) mod n = Suc m mod n"
```
```  1541 proof -
```
```  1542   have "Suc (k * n + m) mod n = (k * n + Suc m) mod n" by simp
```
```  1543   also have "... = Suc m mod n" by (rule mod_mult_self3)
```
```  1544   finally show ?thesis .
```
```  1545 qed
```
```  1546
```
```  1547 lemma mod_Suc_eq_Suc_mod: "Suc m mod n = Suc (m mod n) mod n"
```
```  1548 apply (subst mod_Suc [of m])
```
```  1549 apply (subst mod_Suc [of "m mod n"], simp)
```
```  1550 done
```
```  1551
```
```  1552 lemma mod_2_not_eq_zero_eq_one_nat:
```
```  1553   fixes n :: nat
```
```  1554   shows "n mod 2 \<noteq> 0 \<longleftrightarrow> n mod 2 = 1"
```
```  1555   by (fact not_mod_2_eq_0_eq_1)
```
```  1556
```
```  1557 lemma even_Suc_div_two [simp]:
```
```  1558   "even n \<Longrightarrow> Suc n div 2 = n div 2"
```
```  1559   using even_succ_div_two [of n] by simp
```
```  1560
```
```  1561 lemma odd_Suc_div_two [simp]:
```
```  1562   "odd n \<Longrightarrow> Suc n div 2 = Suc (n div 2)"
```
```  1563   using odd_succ_div_two [of n] by simp
```
```  1564
```
```  1565 lemma odd_two_times_div_two_nat [simp]:
```
```  1566   assumes "odd n"
```
```  1567   shows "2 * (n div 2) = n - (1 :: nat)"
```
```  1568 proof -
```
```  1569   from assms have "2 * (n div 2) + 1 = n"
```
```  1570     by (rule odd_two_times_div_two_succ)
```
```  1571   then have "Suc (2 * (n div 2)) - 1 = n - 1"
```
```  1572     by simp
```
```  1573   then show ?thesis
```
```  1574     by simp
```
```  1575 qed
```
```  1576
```
```  1577 lemma parity_induct [case_names zero even odd]:
```
```  1578   assumes zero: "P 0"
```
```  1579   assumes even: "\<And>n. P n \<Longrightarrow> P (2 * n)"
```
```  1580   assumes odd: "\<And>n. P n \<Longrightarrow> P (Suc (2 * n))"
```
```  1581   shows "P n"
```
```  1582 proof (induct n rule: less_induct)
```
```  1583   case (less n)
```
```  1584   show "P n"
```
```  1585   proof (cases "n = 0")
```
```  1586     case True with zero show ?thesis by simp
```
```  1587   next
```
```  1588     case False
```
```  1589     with less have hyp: "P (n div 2)" by simp
```
```  1590     show ?thesis
```
```  1591     proof (cases "even n")
```
```  1592       case True
```
```  1593       with hyp even [of "n div 2"] show ?thesis
```
```  1594         by simp
```
```  1595     next
```
```  1596       case False
```
```  1597       with hyp odd [of "n div 2"] show ?thesis
```
```  1598         by simp
```
```  1599     qed
```
```  1600   qed
```
```  1601 qed
```
```  1602
```
```  1603 lemma Suc_0_div_numeral [simp]:
```
```  1604   fixes k l :: num
```
```  1605   shows "Suc 0 div numeral k = fst (divmod Num.One k)"
```
```  1606   by (simp_all add: fst_divmod)
```
```  1607
```
```  1608 lemma Suc_0_mod_numeral [simp]:
```
```  1609   fixes k l :: num
```
```  1610   shows "Suc 0 mod numeral k = snd (divmod Num.One k)"
```
```  1611   by (simp_all add: snd_divmod)
```
```  1612
```
```  1613
```
```  1614 subsection \<open>Division on @{typ int}\<close>
```
```  1615
```
```  1616 definition divmod_int_rel :: "int \<Rightarrow> int \<Rightarrow> int \<times> int \<Rightarrow> bool" -- \<open>definition of quotient and remainder\<close>
```
```  1617   where "divmod_int_rel a b = (\<lambda>(q, r). a = b * q + r \<and>
```
```  1618     (if 0 < b then 0 \<le> r \<and> r < b else if b < 0 then b < r \<and> r \<le> 0 else q = 0))"
```
```  1619
```
```  1620 lemma unique_quotient_lemma:
```
```  1621   "b * q' + r' \<le> b * q + r \<Longrightarrow> 0 \<le> r' \<Longrightarrow> r' < b \<Longrightarrow> r < b \<Longrightarrow> q' \<le> (q::int)"
```
```  1622 apply (subgoal_tac "r' + b * (q'-q) \<le> r")
```
```  1623  prefer 2 apply (simp add: right_diff_distrib)
```
```  1624 apply (subgoal_tac "0 < b * (1 + q - q') ")
```
```  1625 apply (erule_tac [2] order_le_less_trans)
```
```  1626  prefer 2 apply (simp add: right_diff_distrib distrib_left)
```
```  1627 apply (subgoal_tac "b * q' < b * (1 + q) ")
```
```  1628  prefer 2 apply (simp add: right_diff_distrib distrib_left)
```
```  1629 apply (simp add: mult_less_cancel_left)
```
```  1630 done
```
```  1631
```
```  1632 lemma unique_quotient_lemma_neg:
```
```  1633   "b * q' + r' \<le> b*q + r \<Longrightarrow> r \<le> 0 \<Longrightarrow> b < r \<Longrightarrow> b < r' \<Longrightarrow> q \<le> (q'::int)"
```
```  1634   by (rule_tac b = "-b" and r = "-r'" and r' = "-r" in unique_quotient_lemma) auto
```
```  1635
```
```  1636 lemma unique_quotient:
```
```  1637   "divmod_int_rel a b (q, r) \<Longrightarrow> divmod_int_rel a b (q', r') \<Longrightarrow> q = q'"
```
```  1638 apply (simp add: divmod_int_rel_def linorder_neq_iff split: split_if_asm)
```
```  1639 apply (blast intro: order_antisym
```
```  1640              dest: order_eq_refl [THEN unique_quotient_lemma]
```
```  1641              order_eq_refl [THEN unique_quotient_lemma_neg] sym)+
```
```  1642 done
```
```  1643
```
```  1644 lemma unique_remainder:
```
```  1645   "divmod_int_rel a b (q, r) \<Longrightarrow> divmod_int_rel a b (q', r') \<Longrightarrow> r = r'"
```
```  1646 apply (subgoal_tac "q = q'")
```
```  1647  apply (simp add: divmod_int_rel_def)
```
```  1648 apply (blast intro: unique_quotient)
```
```  1649 done
```
```  1650
```
```  1651 instantiation int :: Divides.div
```
```  1652 begin
```
```  1653
```
```  1654 definition divide_int
```
```  1655   where "k div l = (if l = 0 \<or> k = 0 then 0
```
```  1656     else if k > 0 \<and> l > 0 \<or> k < 0 \<and> l < 0
```
```  1657       then int (nat \<bar>k\<bar> div nat \<bar>l\<bar>)
```
```  1658       else
```
```  1659         if l dvd k then - int (nat \<bar>k\<bar> div nat \<bar>l\<bar>)
```
```  1660         else - int (Suc (nat \<bar>k\<bar> div nat \<bar>l\<bar>)))"
```
```  1661
```
```  1662 definition mod_int
```
```  1663   where "k mod l = (if l = 0 then k else if l dvd k then 0
```
```  1664     else if k > 0 \<and> l > 0 \<or> k < 0 \<and> l < 0
```
```  1665       then sgn l * int (nat \<bar>k\<bar> mod nat \<bar>l\<bar>)
```
```  1666       else sgn l * (\<bar>l\<bar> - int (nat \<bar>k\<bar> mod nat \<bar>l\<bar>)))"
```
```  1667
```
```  1668 instance ..
```
```  1669
```
```  1670 end
```
```  1671
```
```  1672 lemma divmod_int_rel:
```
```  1673   "divmod_int_rel k l (k div l, k mod l)"
```
```  1674   apply (cases k rule: int_cases3)
```
```  1675   apply (simp add: mod_greater_zero_iff_not_dvd not_le divmod_int_rel_def divide_int_def mod_int_def algebra_simps int_dvd_iff of_nat_mult [symmetric])
```
```  1676   apply (cases l rule: int_cases3)
```
```  1677   apply (simp add: mod_greater_zero_iff_not_dvd not_le divmod_int_rel_def divide_int_def mod_int_def algebra_simps int_dvd_iff of_nat_mult [symmetric])
```
```  1678   apply (simp add: mod_greater_zero_iff_not_dvd not_le divmod_int_rel_def divide_int_def mod_int_def algebra_simps int_dvd_iff of_nat_mult [symmetric])
```
```  1679   apply (simp add: of_nat_add [symmetric])
```
```  1680   apply (simp add: mod_greater_zero_iff_not_dvd not_le divmod_int_rel_def divide_int_def mod_int_def algebra_simps int_dvd_iff of_nat_mult [symmetric])
```
```  1681   apply (simp add: of_nat_add [symmetric])
```
```  1682   apply (cases l rule: int_cases3)
```
```  1683   apply (simp_all add: mod_greater_zero_iff_not_dvd not_le divmod_int_rel_def divide_int_def mod_int_def algebra_simps int_dvd_iff of_nat_mult [symmetric])
```
```  1684   apply (simp_all add: of_nat_add [symmetric])
```
```  1685   done
```
```  1686
```
```  1687 instantiation int :: ring_div
```
```  1688 begin
```
```  1689
```
```  1690 subsubsection \<open>Uniqueness and Monotonicity of Quotients and Remainders\<close>
```
```  1691
```
```  1692 lemma divmod_int_unique:
```
```  1693   assumes "divmod_int_rel k l (q, r)"
```
```  1694   shows div_int_unique: "k div l = q" and mod_int_unique: "k mod l = r"
```
```  1695   using assms divmod_int_rel [of k l]
```
```  1696   using unique_quotient [of k l] unique_remainder [of k l]
```
```  1697   by auto
```
```  1698
```
```  1699 instance
```
```  1700 proof
```
```  1701   fix a b :: int
```
```  1702   show "a div b * b + a mod b = a"
```
```  1703     using divmod_int_rel [of a b]
```
```  1704     unfolding divmod_int_rel_def by (simp add: mult.commute)
```
```  1705 next
```
```  1706   fix a b c :: int
```
```  1707   assume "b \<noteq> 0"
```
```  1708   hence "divmod_int_rel (a + c * b) b (c + a div b, a mod b)"
```
```  1709     using divmod_int_rel [of a b]
```
```  1710     unfolding divmod_int_rel_def by (auto simp: algebra_simps)
```
```  1711   thus "(a + c * b) div b = c + a div b"
```
```  1712     by (rule div_int_unique)
```
```  1713 next
```
```  1714   fix a b c :: int
```
```  1715   assume "c \<noteq> 0"
```
```  1716   hence "\<And>q r. divmod_int_rel a b (q, r)
```
```  1717     \<Longrightarrow> divmod_int_rel (c * a) (c * b) (q, c * r)"
```
```  1718     unfolding divmod_int_rel_def
```
```  1719     by - (rule linorder_cases [of 0 b], auto simp: algebra_simps
```
```  1720       mult_less_0_iff zero_less_mult_iff mult_strict_right_mono
```
```  1721       mult_strict_right_mono_neg zero_le_mult_iff mult_le_0_iff)
```
```  1722   hence "divmod_int_rel (c * a) (c * b) (a div b, c * (a mod b))"
```
```  1723     using divmod_int_rel [of a b] .
```
```  1724   thus "(c * a) div (c * b) = a div b"
```
```  1725     by (rule div_int_unique)
```
```  1726 next
```
```  1727   fix a :: int show "a div 0 = 0"
```
```  1728     by (rule div_int_unique, simp add: divmod_int_rel_def)
```
```  1729 next
```
```  1730   fix a :: int show "0 div a = 0"
```
```  1731     by (rule div_int_unique, auto simp add: divmod_int_rel_def)
```
```  1732 qed
```
```  1733
```
```  1734 end
```
```  1735
```
```  1736 lemma is_unit_int:
```
```  1737   "is_unit (k::int) \<longleftrightarrow> k = 1 \<or> k = - 1"
```
```  1738   by auto
```
```  1739
```
```  1740 instantiation int :: normalization_semidom
```
```  1741 begin
```
```  1742
```
```  1743 definition normalize_int
```
```  1744   where [simp]: "normalize = (abs :: int \<Rightarrow> int)"
```
```  1745
```
```  1746 definition unit_factor_int
```
```  1747   where [simp]: "unit_factor = (sgn :: int \<Rightarrow> int)"
```
```  1748
```
```  1749 instance
```
```  1750 proof
```
```  1751   fix k :: int
```
```  1752   assume "k \<noteq> 0"
```
```  1753   then have "\<bar>sgn k\<bar> = 1"
```
```  1754     by (cases "0::int" k rule: linorder_cases) simp_all
```
```  1755   then show "is_unit (unit_factor k)"
```
```  1756     by simp
```
```  1757 qed (simp_all add: sgn_times mult_sgn_abs)
```
```  1758
```
```  1759 end
```
```  1760
```
```  1761 text\<open>Basic laws about division and remainder\<close>
```
```  1762
```
```  1763 lemma zmod_zdiv_equality: "(a::int) = b * (a div b) + (a mod b)"
```
```  1764   by (fact mod_div_equality2 [symmetric])
```
```  1765
```
```  1766 lemma zdiv_int: "int (a div b) = int a div int b"
```
```  1767   by (simp add: divide_int_def)
```
```  1768
```
```  1769 lemma zmod_int: "int (a mod b) = int a mod int b"
```
```  1770   by (simp add: mod_int_def int_dvd_iff)
```
```  1771
```
```  1772 text \<open>Tool setup\<close>
```
```  1773
```
```  1774 ML \<open>
```
```  1775 structure Cancel_Div_Mod_Int = Cancel_Div_Mod
```
```  1776 (
```
```  1777   val div_name = @{const_name Rings.divide};
```
```  1778   val mod_name = @{const_name mod};
```
```  1779   val mk_binop = HOLogic.mk_binop;
```
```  1780   val mk_sum = Arith_Data.mk_sum HOLogic.intT;
```
```  1781   val dest_sum = Arith_Data.dest_sum;
```
```  1782
```
```  1783   val div_mod_eqs = map mk_meta_eq [@{thm div_mod_equality}, @{thm div_mod_equality2}];
```
```  1784
```
```  1785   val prove_eq_sums = Arith_Data.prove_conv2 all_tac (Arith_Data.simp_all_tac
```
```  1786     (@{thm diff_conv_add_uminus} :: @{thms add_0_left add_0_right} @ @{thms ac_simps}))
```
```  1787 )
```
```  1788 \<close>
```
```  1789
```
```  1790 simproc_setup cancel_div_mod_int ("(k::int) + l") = \<open>K Cancel_Div_Mod_Int.proc\<close>
```
```  1791
```
```  1792 lemma pos_mod_conj: "(0::int) < b \<Longrightarrow> 0 \<le> a mod b \<and> a mod b < b"
```
```  1793   using divmod_int_rel [of a b]
```
```  1794   by (auto simp add: divmod_int_rel_def prod_eq_iff)
```
```  1795
```
```  1796 lemmas pos_mod_sign [simp] = pos_mod_conj [THEN conjunct1]
```
```  1797    and pos_mod_bound [simp] = pos_mod_conj [THEN conjunct2]
```
```  1798
```
```  1799 lemma neg_mod_conj: "b < (0::int) \<Longrightarrow> a mod b \<le> 0 \<and> b < a mod b"
```
```  1800   using divmod_int_rel [of a b]
```
```  1801   by (auto simp add: divmod_int_rel_def prod_eq_iff)
```
```  1802
```
```  1803 lemmas neg_mod_sign [simp] = neg_mod_conj [THEN conjunct1]
```
```  1804    and neg_mod_bound [simp] = neg_mod_conj [THEN conjunct2]
```
```  1805
```
```  1806
```
```  1807 subsubsection \<open>General Properties of div and mod\<close>
```
```  1808
```
```  1809 lemma div_pos_pos_trivial: "[| (0::int) \<le> a;  a < b |] ==> a div b = 0"
```
```  1810 apply (rule div_int_unique)
```
```  1811 apply (auto simp add: divmod_int_rel_def)
```
```  1812 done
```
```  1813
```
```  1814 lemma div_neg_neg_trivial: "[| a \<le> (0::int);  b < a |] ==> a div b = 0"
```
```  1815 apply (rule div_int_unique)
```
```  1816 apply (auto simp add: divmod_int_rel_def)
```
```  1817 done
```
```  1818
```
```  1819 lemma div_pos_neg_trivial: "[| (0::int) < a;  a+b \<le> 0 |] ==> a div b = -1"
```
```  1820 apply (rule div_int_unique)
```
```  1821 apply (auto simp add: divmod_int_rel_def)
```
```  1822 done
```
```  1823
```
```  1824 (*There is no div_neg_pos_trivial because  0 div b = 0 would supersede it*)
```
```  1825
```
```  1826 lemma mod_pos_pos_trivial: "[| (0::int) \<le> a;  a < b |] ==> a mod b = a"
```
```  1827 apply (rule_tac q = 0 in mod_int_unique)
```
```  1828 apply (auto simp add: divmod_int_rel_def)
```
```  1829 done
```
```  1830
```
```  1831 lemma mod_neg_neg_trivial: "[| a \<le> (0::int);  b < a |] ==> a mod b = a"
```
```  1832 apply (rule_tac q = 0 in mod_int_unique)
```
```  1833 apply (auto simp add: divmod_int_rel_def)
```
```  1834 done
```
```  1835
```
```  1836 lemma mod_pos_neg_trivial: "[| (0::int) < a;  a+b \<le> 0 |] ==> a mod b = a+b"
```
```  1837 apply (rule_tac q = "-1" in mod_int_unique)
```
```  1838 apply (auto simp add: divmod_int_rel_def)
```
```  1839 done
```
```  1840
```
```  1841 text\<open>There is no @{text mod_neg_pos_trivial}.\<close>
```
```  1842
```
```  1843
```
```  1844 subsubsection \<open>Laws for div and mod with Unary Minus\<close>
```
```  1845
```
```  1846 lemma zminus1_lemma:
```
```  1847      "divmod_int_rel a b (q, r) ==> b \<noteq> 0
```
```  1848       ==> divmod_int_rel (-a) b (if r=0 then -q else -q - 1,
```
```  1849                           if r=0 then 0 else b-r)"
```
```  1850 by (force simp add: split_ifs divmod_int_rel_def linorder_neq_iff right_diff_distrib)
```
```  1851
```
```  1852
```
```  1853 lemma zdiv_zminus1_eq_if:
```
```  1854      "b \<noteq> (0::int)
```
```  1855       ==> (-a) div b =
```
```  1856           (if a mod b = 0 then - (a div b) else  - (a div b) - 1)"
```
```  1857 by (blast intro: divmod_int_rel [THEN zminus1_lemma, THEN div_int_unique])
```
```  1858
```
```  1859 lemma zmod_zminus1_eq_if:
```
```  1860      "(-a::int) mod b = (if a mod b = 0 then 0 else  b - (a mod b))"
```
```  1861 apply (case_tac "b = 0", simp)
```
```  1862 apply (blast intro: divmod_int_rel [THEN zminus1_lemma, THEN mod_int_unique])
```
```  1863 done
```
```  1864
```
```  1865 lemma zmod_zminus1_not_zero:
```
```  1866   fixes k l :: int
```
```  1867   shows "- k mod l \<noteq> 0 \<Longrightarrow> k mod l \<noteq> 0"
```
```  1868   unfolding zmod_zminus1_eq_if by auto
```
```  1869
```
```  1870 lemma zdiv_zminus2_eq_if:
```
```  1871      "b \<noteq> (0::int)
```
```  1872       ==> a div (-b) =
```
```  1873           (if a mod b = 0 then - (a div b) else  - (a div b) - 1)"
```
```  1874 by (simp add: zdiv_zminus1_eq_if div_minus_right)
```
```  1875
```
```  1876 lemma zmod_zminus2_eq_if:
```
```  1877      "a mod (-b::int) = (if a mod b = 0 then 0 else  (a mod b) - b)"
```
```  1878 by (simp add: zmod_zminus1_eq_if mod_minus_right)
```
```  1879
```
```  1880 lemma zmod_zminus2_not_zero:
```
```  1881   fixes k l :: int
```
```  1882   shows "k mod - l \<noteq> 0 \<Longrightarrow> k mod l \<noteq> 0"
```
```  1883   unfolding zmod_zminus2_eq_if by auto
```
```  1884
```
```  1885
```
```  1886 subsubsection \<open>Monotonicity in the First Argument (Dividend)\<close>
```
```  1887
```
```  1888 lemma zdiv_mono1: "[| a \<le> a';  0 < (b::int) |] ==> a div b \<le> a' div b"
```
```  1889 apply (cut_tac a = a and b = b in zmod_zdiv_equality)
```
```  1890 apply (cut_tac a = a' and b = b in zmod_zdiv_equality)
```
```  1891 apply (rule unique_quotient_lemma)
```
```  1892 apply (erule subst)
```
```  1893 apply (erule subst, simp_all)
```
```  1894 done
```
```  1895
```
```  1896 lemma zdiv_mono1_neg: "[| a \<le> a';  (b::int) < 0 |] ==> a' div b \<le> a div b"
```
```  1897 apply (cut_tac a = a and b = b in zmod_zdiv_equality)
```
```  1898 apply (cut_tac a = a' and b = b in zmod_zdiv_equality)
```
```  1899 apply (rule unique_quotient_lemma_neg)
```
```  1900 apply (erule subst)
```
```  1901 apply (erule subst, simp_all)
```
```  1902 done
```
```  1903
```
```  1904
```
```  1905 subsubsection \<open>Monotonicity in the Second Argument (Divisor)\<close>
```
```  1906
```
```  1907 lemma q_pos_lemma:
```
```  1908      "[| 0 \<le> b'*q' + r'; r' < b';  0 < b' |] ==> 0 \<le> (q'::int)"
```
```  1909 apply (subgoal_tac "0 < b'* (q' + 1) ")
```
```  1910  apply (simp add: zero_less_mult_iff)
```
```  1911 apply (simp add: distrib_left)
```
```  1912 done
```
```  1913
```
```  1914 lemma zdiv_mono2_lemma:
```
```  1915      "[| b*q + r = b'*q' + r';  0 \<le> b'*q' + r';
```
```  1916          r' < b';  0 \<le> r;  0 < b';  b' \<le> b |]
```
```  1917       ==> q \<le> (q'::int)"
```
```  1918 apply (frule q_pos_lemma, assumption+)
```
```  1919 apply (subgoal_tac "b*q < b* (q' + 1) ")
```
```  1920  apply (simp add: mult_less_cancel_left)
```
```  1921 apply (subgoal_tac "b*q = r' - r + b'*q'")
```
```  1922  prefer 2 apply simp
```
```  1923 apply (simp (no_asm_simp) add: distrib_left)
```
```  1924 apply (subst add.commute, rule add_less_le_mono, arith)
```
```  1925 apply (rule mult_right_mono, auto)
```
```  1926 done
```
```  1927
```
```  1928 lemma zdiv_mono2:
```
```  1929      "[| (0::int) \<le> a;  0 < b';  b' \<le> b |] ==> a div b \<le> a div b'"
```
```  1930 apply (subgoal_tac "b \<noteq> 0")
```
```  1931  prefer 2 apply arith
```
```  1932 apply (cut_tac a = a and b = b in zmod_zdiv_equality)
```
```  1933 apply (cut_tac a = a and b = b' in zmod_zdiv_equality)
```
```  1934 apply (rule zdiv_mono2_lemma)
```
```  1935 apply (erule subst)
```
```  1936 apply (erule subst, simp_all)
```
```  1937 done
```
```  1938
```
```  1939 lemma q_neg_lemma:
```
```  1940      "[| b'*q' + r' < 0;  0 \<le> r';  0 < b' |] ==> q' \<le> (0::int)"
```
```  1941 apply (subgoal_tac "b'*q' < 0")
```
```  1942  apply (simp add: mult_less_0_iff, arith)
```
```  1943 done
```
```  1944
```
```  1945 lemma zdiv_mono2_neg_lemma:
```
```  1946      "[| b*q + r = b'*q' + r';  b'*q' + r' < 0;
```
```  1947          r < b;  0 \<le> r';  0 < b';  b' \<le> b |]
```
```  1948       ==> q' \<le> (q::int)"
```
```  1949 apply (frule q_neg_lemma, assumption+)
```
```  1950 apply (subgoal_tac "b*q' < b* (q + 1) ")
```
```  1951  apply (simp add: mult_less_cancel_left)
```
```  1952 apply (simp add: distrib_left)
```
```  1953 apply (subgoal_tac "b*q' \<le> b'*q'")
```
```  1954  prefer 2 apply (simp add: mult_right_mono_neg, arith)
```
```  1955 done
```
```  1956
```
```  1957 lemma zdiv_mono2_neg:
```
```  1958      "[| a < (0::int);  0 < b';  b' \<le> b |] ==> a div b' \<le> a div b"
```
```  1959 apply (cut_tac a = a and b = b in zmod_zdiv_equality)
```
```  1960 apply (cut_tac a = a and b = b' in zmod_zdiv_equality)
```
```  1961 apply (rule zdiv_mono2_neg_lemma)
```
```  1962 apply (erule subst)
```
```  1963 apply (erule subst, simp_all)
```
```  1964 done
```
```  1965
```
```  1966
```
```  1967 subsubsection \<open>More Algebraic Laws for div and mod\<close>
```
```  1968
```
```  1969 text\<open>proving (a*b) div c = a * (b div c) + a * (b mod c)\<close>
```
```  1970
```
```  1971 lemma zmult1_lemma:
```
```  1972      "[| divmod_int_rel b c (q, r) |]
```
```  1973       ==> divmod_int_rel (a * b) c (a*q + a*r div c, a*r mod c)"
```
```  1974 by (auto simp add: split_ifs divmod_int_rel_def linorder_neq_iff distrib_left ac_simps)
```
```  1975
```
```  1976 lemma zdiv_zmult1_eq: "(a*b) div c = a*(b div c) + a*(b mod c) div (c::int)"
```
```  1977 apply (case_tac "c = 0", simp)
```
```  1978 apply (blast intro: divmod_int_rel [THEN zmult1_lemma, THEN div_int_unique])
```
```  1979 done
```
```  1980
```
```  1981 text\<open>proving (a+b) div c = a div c + b div c + ((a mod c + b mod c) div c)\<close>
```
```  1982
```
```  1983 lemma zadd1_lemma:
```
```  1984      "[| divmod_int_rel a c (aq, ar);  divmod_int_rel b c (bq, br) |]
```
```  1985       ==> divmod_int_rel (a+b) c (aq + bq + (ar+br) div c, (ar+br) mod c)"
```
```  1986 by (force simp add: split_ifs divmod_int_rel_def linorder_neq_iff distrib_left)
```
```  1987
```
```  1988 (*NOT suitable for rewriting: the RHS has an instance of the LHS*)
```
```  1989 lemma zdiv_zadd1_eq:
```
```  1990      "(a+b) div (c::int) = a div c + b div c + ((a mod c + b mod c) div c)"
```
```  1991 apply (case_tac "c = 0", simp)
```
```  1992 apply (blast intro: zadd1_lemma [OF divmod_int_rel divmod_int_rel] div_int_unique)
```
```  1993 done
```
```  1994
```
```  1995 lemma zmod_eq_0_iff: "(m mod d = 0) = (EX q::int. m = d*q)"
```
```  1996 by (simp add: dvd_eq_mod_eq_0 [symmetric] dvd_def)
```
```  1997
```
```  1998 (* REVISIT: should this be generalized to all semiring_div types? *)
```
```  1999 lemmas zmod_eq_0D [dest!] = zmod_eq_0_iff [THEN iffD1]
```
```  2000
```
```  2001 lemma zmod_zdiv_equality' [nitpick_unfold]:
```
```  2002   "(m::int) mod n = m - (m div n) * n"
```
```  2003   using mod_div_equality [of m n] by arith
```
```  2004
```
```  2005
```
```  2006 subsubsection \<open>Proving  @{term "a div (b * c) = (a div b) div c"}\<close>
```
```  2007
```
```  2008 (*The condition c>0 seems necessary.  Consider that 7 div ~6 = ~2 but
```
```  2009   7 div 2 div ~3 = 3 div ~3 = ~1.  The subcase (a div b) mod c = 0 seems
```
```  2010   to cause particular problems.*)
```
```  2011
```
```  2012 text\<open>first, four lemmas to bound the remainder for the cases b<0 and b>0\<close>
```
```  2013
```
```  2014 lemma zmult2_lemma_aux1: "[| (0::int) < c;  b < r;  r \<le> 0 |] ==> b * c < b * (q mod c) + r"
```
```  2015 apply (subgoal_tac "b * (c - q mod c) < r * 1")
```
```  2016  apply (simp add: algebra_simps)
```
```  2017 apply (rule order_le_less_trans)
```
```  2018  apply (erule_tac [2] mult_strict_right_mono)
```
```  2019  apply (rule mult_left_mono_neg)
```
```  2020   using add1_zle_eq[of "q mod c"]apply(simp add: algebra_simps)
```
```  2021  apply (simp)
```
```  2022 apply (simp)
```
```  2023 done
```
```  2024
```
```  2025 lemma zmult2_lemma_aux2:
```
```  2026      "[| (0::int) < c;   b < r;  r \<le> 0 |] ==> b * (q mod c) + r \<le> 0"
```
```  2027 apply (subgoal_tac "b * (q mod c) \<le> 0")
```
```  2028  apply arith
```
```  2029 apply (simp add: mult_le_0_iff)
```
```  2030 done
```
```  2031
```
```  2032 lemma zmult2_lemma_aux3: "[| (0::int) < c;  0 \<le> r;  r < b |] ==> 0 \<le> b * (q mod c) + r"
```
```  2033 apply (subgoal_tac "0 \<le> b * (q mod c) ")
```
```  2034 apply arith
```
```  2035 apply (simp add: zero_le_mult_iff)
```
```  2036 done
```
```  2037
```
```  2038 lemma zmult2_lemma_aux4: "[| (0::int) < c; 0 \<le> r; r < b |] ==> b * (q mod c) + r < b * c"
```
```  2039 apply (subgoal_tac "r * 1 < b * (c - q mod c) ")
```
```  2040  apply (simp add: right_diff_distrib)
```
```  2041 apply (rule order_less_le_trans)
```
```  2042  apply (erule mult_strict_right_mono)
```
```  2043  apply (rule_tac [2] mult_left_mono)
```
```  2044   apply simp
```
```  2045  using add1_zle_eq[of "q mod c"] apply (simp add: algebra_simps)
```
```  2046 apply simp
```
```  2047 done
```
```  2048
```
```  2049 lemma zmult2_lemma: "[| divmod_int_rel a b (q, r); 0 < c |]
```
```  2050       ==> divmod_int_rel a (b * c) (q div c, b*(q mod c) + r)"
```
```  2051 by (auto simp add: mult.assoc divmod_int_rel_def linorder_neq_iff
```
```  2052                    zero_less_mult_iff distrib_left [symmetric]
```
```  2053                    zmult2_lemma_aux1 zmult2_lemma_aux2 zmult2_lemma_aux3 zmult2_lemma_aux4 mult_less_0_iff split: split_if_asm)
```
```  2054
```
```  2055 lemma zdiv_zmult2_eq:
```
```  2056   fixes a b c :: int
```
```  2057   shows "0 \<le> c \<Longrightarrow> a div (b * c) = (a div b) div c"
```
```  2058 apply (case_tac "b = 0", simp)
```
```  2059 apply (force simp add: le_less divmod_int_rel [THEN zmult2_lemma, THEN div_int_unique])
```
```  2060 done
```
```  2061
```
```  2062 lemma zmod_zmult2_eq:
```
```  2063   fixes a b c :: int
```
```  2064   shows "0 \<le> c \<Longrightarrow> a mod (b * c) = b * (a div b mod c) + a mod b"
```
```  2065 apply (case_tac "b = 0", simp)
```
```  2066 apply (force simp add: le_less divmod_int_rel [THEN zmult2_lemma, THEN mod_int_unique])
```
```  2067 done
```
```  2068
```
```  2069 lemma div_pos_geq:
```
```  2070   fixes k l :: int
```
```  2071   assumes "0 < l" and "l \<le> k"
```
```  2072   shows "k div l = (k - l) div l + 1"
```
```  2073 proof -
```
```  2074   have "k = (k - l) + l" by simp
```
```  2075   then obtain j where k: "k = j + l" ..
```
```  2076   with assms show ?thesis by simp
```
```  2077 qed
```
```  2078
```
```  2079 lemma mod_pos_geq:
```
```  2080   fixes k l :: int
```
```  2081   assumes "0 < l" and "l \<le> k"
```
```  2082   shows "k mod l = (k - l) mod l"
```
```  2083 proof -
```
```  2084   have "k = (k - l) + l" by simp
```
```  2085   then obtain j where k: "k = j + l" ..
```
```  2086   with assms show ?thesis by simp
```
```  2087 qed
```
```  2088
```
```  2089
```
```  2090 subsubsection \<open>Splitting Rules for div and mod\<close>
```
```  2091
```
```  2092 text\<open>The proofs of the two lemmas below are essentially identical\<close>
```
```  2093
```
```  2094 lemma split_pos_lemma:
```
```  2095  "0<k ==>
```
```  2096     P(n div k :: int)(n mod k) = (\<forall>i j. 0\<le>j & j<k & n = k*i + j --> P i j)"
```
```  2097 apply (rule iffI, clarify)
```
```  2098  apply (erule_tac P="P x y" for x y in rev_mp)
```
```  2099  apply (subst mod_add_eq)
```
```  2100  apply (subst zdiv_zadd1_eq)
```
```  2101  apply (simp add: div_pos_pos_trivial mod_pos_pos_trivial)
```
```  2102 txt\<open>converse direction\<close>
```
```  2103 apply (drule_tac x = "n div k" in spec)
```
```  2104 apply (drule_tac x = "n mod k" in spec, simp)
```
```  2105 done
```
```  2106
```
```  2107 lemma split_neg_lemma:
```
```  2108  "k<0 ==>
```
```  2109     P(n div k :: int)(n mod k) = (\<forall>i j. k<j & j\<le>0 & n = k*i + j --> P i j)"
```
```  2110 apply (rule iffI, clarify)
```
```  2111  apply (erule_tac P="P x y" for x y in rev_mp)
```
```  2112  apply (subst mod_add_eq)
```
```  2113  apply (subst zdiv_zadd1_eq)
```
```  2114  apply (simp add: div_neg_neg_trivial mod_neg_neg_trivial)
```
```  2115 txt\<open>converse direction\<close>
```
```  2116 apply (drule_tac x = "n div k" in spec)
```
```  2117 apply (drule_tac x = "n mod k" in spec, simp)
```
```  2118 done
```
```  2119
```
```  2120 lemma split_zdiv:
```
```  2121  "P(n div k :: int) =
```
```  2122   ((k = 0 --> P 0) &
```
```  2123    (0<k --> (\<forall>i j. 0\<le>j & j<k & n = k*i + j --> P i)) &
```
```  2124    (k<0 --> (\<forall>i j. k<j & j\<le>0 & n = k*i + j --> P i)))"
```
```  2125 apply (case_tac "k=0", simp)
```
```  2126 apply (simp only: linorder_neq_iff)
```
```  2127 apply (erule disjE)
```
```  2128  apply (simp_all add: split_pos_lemma [of concl: "%x y. P x"]
```
```  2129                       split_neg_lemma [of concl: "%x y. P x"])
```
```  2130 done
```
```  2131
```
```  2132 lemma split_zmod:
```
```  2133  "P(n mod k :: int) =
```
```  2134   ((k = 0 --> P n) &
```
```  2135    (0<k --> (\<forall>i j. 0\<le>j & j<k & n = k*i + j --> P j)) &
```
```  2136    (k<0 --> (\<forall>i j. k<j & j\<le>0 & n = k*i + j --> P j)))"
```
```  2137 apply (case_tac "k=0", simp)
```
```  2138 apply (simp only: linorder_neq_iff)
```
```  2139 apply (erule disjE)
```
```  2140  apply (simp_all add: split_pos_lemma [of concl: "%x y. P y"]
```
```  2141                       split_neg_lemma [of concl: "%x y. P y"])
```
```  2142 done
```
```  2143
```
```  2144 text \<open>Enable (lin)arith to deal with @{const divide} and @{const mod}
```
```  2145   when these are applied to some constant that is of the form
```
```  2146   @{term "numeral k"}:\<close>
```
```  2147 declare split_zdiv [of _ _ "numeral k", arith_split] for k
```
```  2148 declare split_zmod [of _ _ "numeral k", arith_split] for k
```
```  2149
```
```  2150
```
```  2151 subsubsection \<open>Computing @{text "div"} and @{text "mod"} with shifting\<close>
```
```  2152
```
```  2153 lemma pos_divmod_int_rel_mult_2:
```
```  2154   assumes "0 \<le> b"
```
```  2155   assumes "divmod_int_rel a b (q, r)"
```
```  2156   shows "divmod_int_rel (1 + 2*a) (2*b) (q, 1 + 2*r)"
```
```  2157   using assms unfolding divmod_int_rel_def by auto
```
```  2158
```
```  2159 declaration \<open>K (Lin_Arith.add_simps @{thms uminus_numeral_One})\<close>
```
```  2160
```
```  2161 lemma neg_divmod_int_rel_mult_2:
```
```  2162   assumes "b \<le> 0"
```
```  2163   assumes "divmod_int_rel (a + 1) b (q, r)"
```
```  2164   shows "divmod_int_rel (1 + 2*a) (2*b) (q, 2*r - 1)"
```
```  2165   using assms unfolding divmod_int_rel_def by auto
```
```  2166
```
```  2167 text\<open>computing div by shifting\<close>
```
```  2168
```
```  2169 lemma pos_zdiv_mult_2: "(0::int) \<le> a ==> (1 + 2*b) div (2*a) = b div a"
```
```  2170   using pos_divmod_int_rel_mult_2 [OF _ divmod_int_rel]
```
```  2171   by (rule div_int_unique)
```
```  2172
```
```  2173 lemma neg_zdiv_mult_2:
```
```  2174   assumes A: "a \<le> (0::int)" shows "(1 + 2*b) div (2*a) = (b+1) div a"
```
```  2175   using neg_divmod_int_rel_mult_2 [OF A divmod_int_rel]
```
```  2176   by (rule div_int_unique)
```
```  2177
```
```  2178 (* FIXME: add rules for negative numerals *)
```
```  2179 lemma zdiv_numeral_Bit0 [simp]:
```
```  2180   "numeral (Num.Bit0 v) div numeral (Num.Bit0 w) =
```
```  2181     numeral v div (numeral w :: int)"
```
```  2182   unfolding numeral.simps unfolding mult_2 [symmetric]
```
```  2183   by (rule div_mult_mult1, simp)
```
```  2184
```
```  2185 lemma zdiv_numeral_Bit1 [simp]:
```
```  2186   "numeral (Num.Bit1 v) div numeral (Num.Bit0 w) =
```
```  2187     (numeral v div (numeral w :: int))"
```
```  2188   unfolding numeral.simps
```
```  2189   unfolding mult_2 [symmetric] add.commute [of _ 1]
```
```  2190   by (rule pos_zdiv_mult_2, simp)
```
```  2191
```
```  2192 lemma pos_zmod_mult_2:
```
```  2193   fixes a b :: int
```
```  2194   assumes "0 \<le> a"
```
```  2195   shows "(1 + 2 * b) mod (2 * a) = 1 + 2 * (b mod a)"
```
```  2196   using pos_divmod_int_rel_mult_2 [OF assms divmod_int_rel]
```
```  2197   by (rule mod_int_unique)
```
```  2198
```
```  2199 lemma neg_zmod_mult_2:
```
```  2200   fixes a b :: int
```
```  2201   assumes "a \<le> 0"
```
```  2202   shows "(1 + 2 * b) mod (2 * a) = 2 * ((b + 1) mod a) - 1"
```
```  2203   using neg_divmod_int_rel_mult_2 [OF assms divmod_int_rel]
```
```  2204   by (rule mod_int_unique)
```
```  2205
```
```  2206 (* FIXME: add rules for negative numerals *)
```
```  2207 lemma zmod_numeral_Bit0 [simp]:
```
```  2208   "numeral (Num.Bit0 v) mod numeral (Num.Bit0 w) =
```
```  2209     (2::int) * (numeral v mod numeral w)"
```
```  2210   unfolding numeral_Bit0 [of v] numeral_Bit0 [of w]
```
```  2211   unfolding mult_2 [symmetric] by (rule mod_mult_mult1)
```
```  2212
```
```  2213 lemma zmod_numeral_Bit1 [simp]:
```
```  2214   "numeral (Num.Bit1 v) mod numeral (Num.Bit0 w) =
```
```  2215     2 * (numeral v mod numeral w) + (1::int)"
```
```  2216   unfolding numeral_Bit1 [of v] numeral_Bit0 [of w]
```
```  2217   unfolding mult_2 [symmetric] add.commute [of _ 1]
```
```  2218   by (rule pos_zmod_mult_2, simp)
```
```  2219
```
```  2220 lemma zdiv_eq_0_iff:
```
```  2221  "(i::int) div k = 0 \<longleftrightarrow> k=0 \<or> 0\<le>i \<and> i<k \<or> i\<le>0 \<and> k<i" (is "?L = ?R")
```
```  2222 proof
```
```  2223   assume ?L
```
```  2224   have "?L \<longrightarrow> ?R" by (rule split_zdiv[THEN iffD2]) simp
```
```  2225   with \<open>?L\<close> show ?R by blast
```
```  2226 next
```
```  2227   assume ?R thus ?L
```
```  2228     by(auto simp: div_pos_pos_trivial div_neg_neg_trivial)
```
```  2229 qed
```
```  2230
```
```  2231
```
```  2232 subsubsection \<open>Quotients of Signs\<close>
```
```  2233
```
```  2234 lemma div_eq_minus1: "(0::int) < b ==> -1 div b = -1"
```
```  2235 by (simp add: divide_int_def)
```
```  2236
```
```  2237 lemma zmod_minus1: "(0::int) < b ==> -1 mod b = b - 1"
```
```  2238 by (simp add: mod_int_def)
```
```  2239
```
```  2240 lemma div_neg_pos_less0: "[| a < (0::int);  0 < b |] ==> a div b < 0"
```
```  2241 apply (subgoal_tac "a div b \<le> -1", force)
```
```  2242 apply (rule order_trans)
```
```  2243 apply (rule_tac a' = "-1" in zdiv_mono1)
```
```  2244 apply (auto simp add: div_eq_minus1)
```
```  2245 done
```
```  2246
```
```  2247 lemma div_nonneg_neg_le0: "[| (0::int) \<le> a; b < 0 |] ==> a div b \<le> 0"
```
```  2248 by (drule zdiv_mono1_neg, auto)
```
```  2249
```
```  2250 lemma div_nonpos_pos_le0: "[| (a::int) \<le> 0; b > 0 |] ==> a div b \<le> 0"
```
```  2251 by (drule zdiv_mono1, auto)
```
```  2252
```
```  2253 text\<open>Now for some equivalences of the form @{text"a div b >=< 0 \<longleftrightarrow> \<dots>"}
```
```  2254 conditional upon the sign of @{text a} or @{text b}. There are many more.
```
```  2255 They should all be simp rules unless that causes too much search.\<close>
```
```  2256
```
```  2257 lemma pos_imp_zdiv_nonneg_iff: "(0::int) < b ==> (0 \<le> a div b) = (0 \<le> a)"
```
```  2258 apply auto
```
```  2259 apply (drule_tac [2] zdiv_mono1)
```
```  2260 apply (auto simp add: linorder_neq_iff)
```
```  2261 apply (simp (no_asm_use) add: linorder_not_less [symmetric])
```
```  2262 apply (blast intro: div_neg_pos_less0)
```
```  2263 done
```
```  2264
```
```  2265 lemma pos_imp_zdiv_pos_iff:
```
```  2266   "0<k \<Longrightarrow> 0 < (i::int) div k \<longleftrightarrow> k \<le> i"
```
```  2267 using pos_imp_zdiv_nonneg_iff[of k i] zdiv_eq_0_iff[of i k]
```
```  2268 by arith
```
```  2269
```
```  2270 lemma neg_imp_zdiv_nonneg_iff:
```
```  2271   "b < (0::int) ==> (0 \<le> a div b) = (a \<le> (0::int))"
```
```  2272 apply (subst div_minus_minus [symmetric])
```
```  2273 apply (subst pos_imp_zdiv_nonneg_iff, auto)
```
```  2274 done
```
```  2275
```
```  2276 (*But not (a div b \<le> 0 iff a\<le>0); consider a=1, b=2 when a div b = 0.*)
```
```  2277 lemma pos_imp_zdiv_neg_iff: "(0::int) < b ==> (a div b < 0) = (a < 0)"
```
```  2278 by (simp add: linorder_not_le [symmetric] pos_imp_zdiv_nonneg_iff)
```
```  2279
```
```  2280 (*Again the law fails for \<le>: consider a = -1, b = -2 when a div b = 0*)
```
```  2281 lemma neg_imp_zdiv_neg_iff: "b < (0::int) ==> (a div b < 0) = (0 < a)"
```
```  2282 by (simp add: linorder_not_le [symmetric] neg_imp_zdiv_nonneg_iff)
```
```  2283
```
```  2284 lemma nonneg1_imp_zdiv_pos_iff:
```
```  2285   "(0::int) <= a \<Longrightarrow> (a div b > 0) = (a >= b & b>0)"
```
```  2286 apply rule
```
```  2287  apply rule
```
```  2288   using div_pos_pos_trivial[of a b]apply arith
```
```  2289  apply(cases "b=0")apply simp
```
```  2290  using div_nonneg_neg_le0[of a b]apply arith
```
```  2291 using int_one_le_iff_zero_less[of "a div b"] zdiv_mono1[of b a b]apply simp
```
```  2292 done
```
```  2293
```
```  2294 lemma zmod_le_nonneg_dividend: "(m::int) \<ge> 0 ==> m mod k \<le> m"
```
```  2295 apply (rule split_zmod[THEN iffD2])
```
```  2296 apply(fastforce dest: q_pos_lemma intro: split_mult_pos_le)
```
```  2297 done
```
```  2298
```
```  2299 lemma zmult_div_cancel:
```
```  2300   "(n::int) * (m div n) = m - (m mod n)"
```
```  2301   using zmod_zdiv_equality [where a="m" and b="n"]
```
```  2302   by (simp add: algebra_simps) (* FIXME: generalize *)
```
```  2303
```
```  2304
```
```  2305 subsubsection \<open>Computation of Division and Remainder\<close>
```
```  2306
```
```  2307 instance int :: semiring_numeral_div
```
```  2308   by intro_classes (auto intro: zmod_le_nonneg_dividend
```
```  2309     simp add:
```
```  2310     zmult_div_cancel
```
```  2311     pos_imp_zdiv_pos_iff div_pos_pos_trivial mod_pos_pos_trivial
```
```  2312     zmod_zmult2_eq zdiv_zmult2_eq)
```
```  2313
```
```  2314 context
```
```  2315 begin
```
```  2316
```
```  2317 qualified definition adjust_div :: "int \<times> int \<Rightarrow> int"
```
```  2318 where
```
```  2319   "adjust_div qr = (let (q, r) = qr in q + of_bool (r \<noteq> 0))"
```
```  2320
```
```  2321 qualified lemma adjust_div_eq [simp, code]:
```
```  2322   "adjust_div (q, r) = q + of_bool (r \<noteq> 0)"
```
```  2323   by (simp add: adjust_div_def)
```
```  2324
```
```  2325 qualified definition adjust_mod :: "int \<Rightarrow> int \<Rightarrow> int"
```
```  2326 where
```
```  2327   [simp]: "adjust_mod l r = (if r = 0 then 0 else l - r)"
```
```  2328
```
```  2329 lemma minus_numeral_div_numeral [simp]:
```
```  2330   "- numeral m div numeral n = - (adjust_div (divmod m n) :: int)"
```
```  2331 proof -
```
```  2332   have "int (fst (divmod m n)) = fst (divmod m n)"
```
```  2333     by (simp only: fst_divmod divide_int_def) auto
```
```  2334   then show ?thesis
```
```  2335     by (auto simp add: split_def Let_def adjust_div_def divides_aux_def divide_int_def)
```
```  2336 qed
```
```  2337
```
```  2338 lemma minus_numeral_mod_numeral [simp]:
```
```  2339   "- numeral m mod numeral n = adjust_mod (numeral n) (snd (divmod m n) :: int)"
```
```  2340 proof -
```
```  2341   have "int (snd (divmod m n)) = snd (divmod m n)" if "snd (divmod m n) \<noteq> (0::int)"
```
```  2342     using that by (simp only: snd_divmod mod_int_def) auto
```
```  2343   then show ?thesis
```
```  2344     by (auto simp add: split_def Let_def adjust_div_def divides_aux_def mod_int_def)
```
```  2345 qed
```
```  2346
```
```  2347 lemma numeral_div_minus_numeral [simp]:
```
```  2348   "numeral m div - numeral n = - (adjust_div (divmod m n) :: int)"
```
```  2349 proof -
```
```  2350   have "int (fst (divmod m n)) = fst (divmod m n)"
```
```  2351     by (simp only: fst_divmod divide_int_def) auto
```
```  2352   then show ?thesis
```
```  2353     by (auto simp add: split_def Let_def adjust_div_def divides_aux_def divide_int_def)
```
```  2354 qed
```
```  2355
```
```  2356 lemma numeral_mod_minus_numeral [simp]:
```
```  2357   "numeral m mod - numeral n = - adjust_mod (numeral n) (snd (divmod m n) :: int)"
```
```  2358 proof -
```
```  2359   have "int (snd (divmod m n)) = snd (divmod m n)" if "snd (divmod m n) \<noteq> (0::int)"
```
```  2360     using that by (simp only: snd_divmod mod_int_def) auto
```
```  2361   then show ?thesis
```
```  2362     by (auto simp add: split_def Let_def adjust_div_def divides_aux_def mod_int_def)
```
```  2363 qed
```
```  2364
```
```  2365 lemma minus_one_div_numeral [simp]:
```
```  2366   "- 1 div numeral n = - (adjust_div (divmod Num.One n) :: int)"
```
```  2367   using minus_numeral_div_numeral [of Num.One n] by simp
```
```  2368
```
```  2369 lemma minus_one_mod_numeral [simp]:
```
```  2370   "- 1 mod numeral n = adjust_mod (numeral n) (snd (divmod Num.One n) :: int)"
```
```  2371   using minus_numeral_mod_numeral [of Num.One n] by simp
```
```  2372
```
```  2373 lemma one_div_minus_numeral [simp]:
```
```  2374   "1 div - numeral n = - (adjust_div (divmod Num.One n) :: int)"
```
```  2375   using numeral_div_minus_numeral [of Num.One n] by simp
```
```  2376
```
```  2377 lemma one_mod_minus_numeral [simp]:
```
```  2378   "1 mod - numeral n = - adjust_mod (numeral n) (snd (divmod Num.One n) :: int)"
```
```  2379   using numeral_mod_minus_numeral [of Num.One n] by simp
```
```  2380
```
```  2381 end
```
```  2382
```
```  2383
```
```  2384 subsubsection \<open>Further properties\<close>
```
```  2385
```
```  2386 text \<open>Simplify expresions in which div and mod combine numerical constants\<close>
```
```  2387
```
```  2388 lemma int_div_pos_eq: "\<lbrakk>(a::int) = b * q + r; 0 \<le> r; r < b\<rbrakk> \<Longrightarrow> a div b = q"
```
```  2389   by (rule div_int_unique [of a b q r]) (simp add: divmod_int_rel_def)
```
```  2390
```
```  2391 lemma int_div_neg_eq: "\<lbrakk>(a::int) = b * q + r; r \<le> 0; b < r\<rbrakk> \<Longrightarrow> a div b = q"
```
```  2392   by (rule div_int_unique [of a b q r],
```
```  2393     simp add: divmod_int_rel_def)
```
```  2394
```
```  2395 lemma int_mod_pos_eq: "\<lbrakk>(a::int) = b * q + r; 0 \<le> r; r < b\<rbrakk> \<Longrightarrow> a mod b = r"
```
```  2396   by (rule mod_int_unique [of a b q r],
```
```  2397     simp add: divmod_int_rel_def)
```
```  2398
```
```  2399 lemma int_mod_neg_eq: "\<lbrakk>(a::int) = b * q + r; r \<le> 0; b < r\<rbrakk> \<Longrightarrow> a mod b = r"
```
```  2400   by (rule mod_int_unique [of a b q r],
```
```  2401     simp add: divmod_int_rel_def)
```
```  2402
```
```  2403 lemma abs_div: "(y::int) dvd x \<Longrightarrow> abs (x div y) = abs x div abs y"
```
```  2404 by (unfold dvd_def, cases "y=0", auto simp add: abs_mult)
```
```  2405
```
```  2406 text\<open>Suggested by Matthias Daum\<close>
```
```  2407 lemma int_power_div_base:
```
```  2408      "\<lbrakk>0 < m; 0 < k\<rbrakk> \<Longrightarrow> k ^ m div k = (k::int) ^ (m - Suc 0)"
```
```  2409 apply (subgoal_tac "k ^ m = k ^ ((m - Suc 0) + Suc 0)")
```
```  2410  apply (erule ssubst)
```
```  2411  apply (simp only: power_add)
```
```  2412  apply simp_all
```
```  2413 done
```
```  2414
```
```  2415 text \<open>by Brian Huffman\<close>
```
```  2416 lemma zminus_zmod: "- ((x::int) mod m) mod m = - x mod m"
```
```  2417 by (rule mod_minus_eq [symmetric])
```
```  2418
```
```  2419 lemma zdiff_zmod_left: "(x mod m - y) mod m = (x - y) mod (m::int)"
```
```  2420 by (rule mod_diff_left_eq [symmetric])
```
```  2421
```
```  2422 lemma zdiff_zmod_right: "(x - y mod m) mod m = (x - y) mod (m::int)"
```
```  2423 by (rule mod_diff_right_eq [symmetric])
```
```  2424
```
```  2425 lemmas zmod_simps =
```
```  2426   mod_add_left_eq  [symmetric]
```
```  2427   mod_add_right_eq [symmetric]
```
```  2428   mod_mult_right_eq[symmetric]
```
```  2429   mod_mult_left_eq [symmetric]
```
```  2430   power_mod
```
```  2431   zminus_zmod zdiff_zmod_left zdiff_zmod_right
```
```  2432
```
```  2433 text \<open>Distributive laws for function @{text nat}.\<close>
```
```  2434
```
```  2435 lemma nat_div_distrib: "0 \<le> x \<Longrightarrow> nat (x div y) = nat x div nat y"
```
```  2436 apply (rule linorder_cases [of y 0])
```
```  2437 apply (simp add: div_nonneg_neg_le0)
```
```  2438 apply simp
```
```  2439 apply (simp add: nat_eq_iff pos_imp_zdiv_nonneg_iff zdiv_int)
```
```  2440 done
```
```  2441
```
```  2442 (*Fails if y<0: the LHS collapses to (nat z) but the RHS doesn't*)
```
```  2443 lemma nat_mod_distrib:
```
```  2444   "\<lbrakk>0 \<le> x; 0 \<le> y\<rbrakk> \<Longrightarrow> nat (x mod y) = nat x mod nat y"
```
```  2445 apply (case_tac "y = 0", simp)
```
```  2446 apply (simp add: nat_eq_iff zmod_int)
```
```  2447 done
```
```  2448
```
```  2449 text  \<open>transfer setup\<close>
```
```  2450
```
```  2451 lemma transfer_nat_int_functions:
```
```  2452     "(x::int) >= 0 \<Longrightarrow> y >= 0 \<Longrightarrow> (nat x) div (nat y) = nat (x div y)"
```
```  2453     "(x::int) >= 0 \<Longrightarrow> y >= 0 \<Longrightarrow> (nat x) mod (nat y) = nat (x mod y)"
```
```  2454   by (auto simp add: nat_div_distrib nat_mod_distrib)
```
```  2455
```
```  2456 lemma transfer_nat_int_function_closures:
```
```  2457     "(x::int) >= 0 \<Longrightarrow> y >= 0 \<Longrightarrow> x div y >= 0"
```
```  2458     "(x::int) >= 0 \<Longrightarrow> y >= 0 \<Longrightarrow> x mod y >= 0"
```
```  2459   apply (cases "y = 0")
```
```  2460   apply (auto simp add: pos_imp_zdiv_nonneg_iff)
```
```  2461   apply (cases "y = 0")
```
```  2462   apply auto
```
```  2463 done
```
```  2464
```
```  2465 declare transfer_morphism_nat_int [transfer add return:
```
```  2466   transfer_nat_int_functions
```
```  2467   transfer_nat_int_function_closures
```
```  2468 ]
```
```  2469
```
```  2470 lemma transfer_int_nat_functions:
```
```  2471     "(int x) div (int y) = int (x div y)"
```
```  2472     "(int x) mod (int y) = int (x mod y)"
```
```  2473   by (auto simp add: zdiv_int zmod_int)
```
```  2474
```
```  2475 lemma transfer_int_nat_function_closures:
```
```  2476     "is_nat x \<Longrightarrow> is_nat y \<Longrightarrow> is_nat (x div y)"
```
```  2477     "is_nat x \<Longrightarrow> is_nat y \<Longrightarrow> is_nat (x mod y)"
```
```  2478   by (simp_all only: is_nat_def transfer_nat_int_function_closures)
```
```  2479
```
```  2480 declare transfer_morphism_int_nat [transfer add return:
```
```  2481   transfer_int_nat_functions
```
```  2482   transfer_int_nat_function_closures
```
```  2483 ]
```
```  2484
```
```  2485 text\<open>Suggested by Matthias Daum\<close>
```
```  2486 lemma int_div_less_self: "\<lbrakk>0 < x; 1 < k\<rbrakk> \<Longrightarrow> x div k < (x::int)"
```
```  2487 apply (subgoal_tac "nat x div nat k < nat x")
```
```  2488  apply (simp add: nat_div_distrib [symmetric])
```
```  2489 apply (rule Divides.div_less_dividend, simp_all)
```
```  2490 done
```
```  2491
```
```  2492 lemma zmod_eq_dvd_iff: "(x::int) mod n = y mod n \<longleftrightarrow> n dvd x - y"
```
```  2493 proof
```
```  2494   assume H: "x mod n = y mod n"
```
```  2495   hence "x mod n - y mod n = 0" by simp
```
```  2496   hence "(x mod n - y mod n) mod n = 0" by simp
```
```  2497   hence "(x - y) mod n = 0" by (simp add: mod_diff_eq[symmetric])
```
```  2498   thus "n dvd x - y" by (simp add: dvd_eq_mod_eq_0)
```
```  2499 next
```
```  2500   assume H: "n dvd x - y"
```
```  2501   then obtain k where k: "x-y = n*k" unfolding dvd_def by blast
```
```  2502   hence "x = n*k + y" by simp
```
```  2503   hence "x mod n = (n*k + y) mod n" by simp
```
```  2504   thus "x mod n = y mod n" by (simp add: mod_add_left_eq)
```
```  2505 qed
```
```  2506
```
```  2507 lemma nat_mod_eq_lemma: assumes xyn: "(x::nat) mod n = y  mod n" and xy:"y \<le> x"
```
```  2508   shows "\<exists>q. x = y + n * q"
```
```  2509 proof-
```
```  2510   from xy have th: "int x - int y = int (x - y)" by simp
```
```  2511   from xyn have "int x mod int n = int y mod int n"
```
```  2512     by (simp add: zmod_int [symmetric])
```
```  2513   hence "int n dvd int x - int y" by (simp only: zmod_eq_dvd_iff[symmetric])
```
```  2514   hence "n dvd x - y" by (simp add: th zdvd_int)
```
```  2515   then show ?thesis using xy unfolding dvd_def apply clarsimp apply (rule_tac x="k" in exI) by arith
```
```  2516 qed
```
```  2517
```
```  2518 lemma nat_mod_eq_iff: "(x::nat) mod n = y mod n \<longleftrightarrow> (\<exists>q1 q2. x + n * q1 = y + n * q2)"
```
```  2519   (is "?lhs = ?rhs")
```
```  2520 proof
```
```  2521   assume H: "x mod n = y mod n"
```
```  2522   {assume xy: "x \<le> y"
```
```  2523     from H have th: "y mod n = x mod n" by simp
```
```  2524     from nat_mod_eq_lemma[OF th xy] have ?rhs
```
```  2525       apply clarify  apply (rule_tac x="q" in exI) by (rule exI[where x="0"], simp)}
```
```  2526   moreover
```
```  2527   {assume xy: "y \<le> x"
```
```  2528     from nat_mod_eq_lemma[OF H xy] have ?rhs
```
```  2529       apply clarify  apply (rule_tac x="0" in exI) by (rule_tac x="q" in exI, simp)}
```
```  2530   ultimately  show ?rhs using linear[of x y] by blast
```
```  2531 next
```
```  2532   assume ?rhs then obtain q1 q2 where q12: "x + n * q1 = y + n * q2" by blast
```
```  2533   hence "(x + n * q1) mod n = (y + n * q2) mod n" by simp
```
```  2534   thus  ?lhs by simp
```
```  2535 qed
```
```  2536
```
```  2537 subsubsection \<open>Dedicated simproc for calculation\<close>
```
```  2538
```
```  2539 text \<open>
```
```  2540   There is space for improvement here: the calculation itself
```
```  2541   could be carried outside the logic, and a generic simproc
```
```  2542   (simplifier setup) for generic calculation would be helpful.
```
```  2543 \<close>
```
```  2544
```
```  2545 simproc_setup numeral_divmod
```
```  2546   ("0 div 0 :: 'a :: semiring_numeral_div" | "0 mod 0 :: 'a :: semiring_numeral_div" |
```
```  2547    "0 div 1 :: 'a :: semiring_numeral_div" | "0 mod 1 :: 'a :: semiring_numeral_div" |
```
```  2548    "0 div - 1 :: int" | "0 mod - 1 :: int" |
```
```  2549    "0 div numeral b :: 'a :: semiring_numeral_div" | "0 mod numeral b :: 'a :: semiring_numeral_div" |
```
```  2550    "0 div - numeral b :: int" | "0 mod - numeral b :: int" |
```
```  2551    "1 div 0 :: 'a :: semiring_numeral_div" | "1 mod 0 :: 'a :: semiring_numeral_div" |
```
```  2552    "1 div 1 :: 'a :: semiring_numeral_div" | "1 mod 1 :: 'a :: semiring_numeral_div" |
```
```  2553    "1 div - 1 :: int" | "1 mod - 1 :: int" |
```
```  2554    "1 div numeral b :: 'a :: semiring_numeral_div" | "1 mod numeral b :: 'a :: semiring_numeral_div" |
```
```  2555    "1 div - numeral b :: int" |"1 mod - numeral b :: int" |
```
```  2556    "- 1 div 0 :: int" | "- 1 mod 0 :: int" | "- 1 div 1 :: int" | "- 1 mod 1 :: int" |
```
```  2557    "- 1 div - 1 :: int" | "- 1 mod - 1 :: int" | "- 1 div numeral b :: int" | "- 1 mod numeral b :: int" |
```
```  2558    "- 1 div - numeral b :: int" | "- 1 mod - numeral b :: int" |
```
```  2559    "numeral a div 0 :: 'a :: semiring_numeral_div" | "numeral a mod 0 :: 'a :: semiring_numeral_div" |
```
```  2560    "numeral a div 1 :: 'a :: semiring_numeral_div" | "numeral a mod 1 :: 'a :: semiring_numeral_div" |
```
```  2561    "numeral a div - 1 :: int" | "numeral a mod - 1 :: int" |
```
```  2562    "numeral a div numeral b :: 'a :: semiring_numeral_div" | "numeral a mod numeral b :: 'a :: semiring_numeral_div" |
```
```  2563    "numeral a div - numeral b :: int" | "numeral a mod - numeral b :: int" |
```
```  2564    "- numeral a div 0 :: int" | "- numeral a mod 0 :: int" |
```
```  2565    "- numeral a div 1 :: int" | "- numeral a mod 1 :: int" |
```
```  2566    "- numeral a div - 1 :: int" | "- numeral a mod - 1 :: int" |
```
```  2567    "- numeral a div numeral b :: int" | "- numeral a mod numeral b :: int" |
```
```  2568    "- numeral a div - numeral b :: int" | "- numeral a mod - numeral b :: int") =
```
```  2569 \<open> let
```
```  2570     val if_cong = the (Code.get_case_cong @{theory} @{const_name If});
```
```  2571     fun successful_rewrite ctxt ct =
```
```  2572       let
```
```  2573         val thm = Simplifier.rewrite ctxt ct
```
```  2574       in if Thm.is_reflexive thm then NONE else SOME thm end;
```
```  2575   in fn phi =>
```
```  2576     let
```
```  2577       val simps = Morphism.fact phi (@{thms div_0 mod_0 div_by_0 mod_by_0 div_by_1 mod_by_1
```
```  2578         one_div_numeral one_mod_numeral minus_one_div_numeral minus_one_mod_numeral
```
```  2579         one_div_minus_numeral one_mod_minus_numeral
```
```  2580         numeral_div_numeral numeral_mod_numeral minus_numeral_div_numeral minus_numeral_mod_numeral
```
```  2581         numeral_div_minus_numeral numeral_mod_minus_numeral
```
```  2582         div_minus_minus mod_minus_minus Divides.adjust_div_eq of_bool_eq one_neq_zero
```
```  2583         numeral_neq_zero neg_equal_0_iff_equal arith_simps arith_special divmod_trivial
```
```  2584         divmod_cancel divmod_steps divmod_step_eq fst_conv snd_conv numeral_One
```
```  2585         case_prod_beta rel_simps Divides.adjust_mod_def div_minus1_right mod_minus1_right
```
```  2586         minus_minus numeral_times_numeral mult_zero_right mult_1_right}
```
```  2587         @ [@{lemma "0 = 0 \<longleftrightarrow> True" by simp}]);
```
```  2588       fun prepare_simpset ctxt = HOL_ss |> Simplifier.simpset_map ctxt
```
```  2589         (Simplifier.add_cong if_cong #> fold Simplifier.add_simp simps)
```
```  2590     in fn ctxt => successful_rewrite (Simplifier.put_simpset (prepare_simpset ctxt) ctxt) end
```
```  2591   end;
```
```  2592 \<close>
```
```  2593
```
```  2594
```
```  2595 subsubsection \<open>Code generation\<close>
```
```  2596
```
```  2597 lemma [code]:
```
```  2598   fixes k :: int
```
```  2599   shows
```
```  2600     "k div 0 = 0"
```
```  2601     "k mod 0 = k"
```
```  2602     "0 div k = 0"
```
```  2603     "0 mod k = 0"
```
```  2604     "k div Int.Pos Num.One = k"
```
```  2605     "k mod Int.Pos Num.One = 0"
```
```  2606     "k div Int.Neg Num.One = - k"
```
```  2607     "k mod Int.Neg Num.One = 0"
```
```  2608     "Int.Pos m div Int.Pos n = (fst (divmod m n) :: int)"
```
```  2609     "Int.Pos m mod Int.Pos n = (snd (divmod m n) :: int)"
```
```  2610     "Int.Neg m div Int.Pos n = - (Divides.adjust_div (divmod m n) :: int)"
```
```  2611     "Int.Neg m mod Int.Pos n = Divides.adjust_mod (Int.Pos n) (snd (divmod m n) :: int)"
```
```  2612     "Int.Pos m div Int.Neg n = - (Divides.adjust_div (divmod m n) :: int)"
```
```  2613     "Int.Pos m mod Int.Neg n = - Divides.adjust_mod (Int.Pos n) (snd (divmod m n) :: int)"
```
```  2614     "Int.Neg m div Int.Neg n = (fst (divmod m n) :: int)"
```
```  2615     "Int.Neg m mod Int.Neg n = - (snd (divmod m n) :: int)"
```
```  2616   by simp_all
```
```  2617
```
```  2618 code_identifier
```
```  2619   code_module Divides \<rightharpoonup> (SML) Arith and (OCaml) Arith and (Haskell) Arith
```
```  2620
```
```  2621 lemma dvd_eq_mod_eq_0_numeral:
```
```  2622   "numeral x dvd (numeral y :: 'a) \<longleftrightarrow> numeral y mod numeral x = (0 :: 'a::semiring_div)"
```
```  2623   by (fact dvd_eq_mod_eq_0)
```
```  2624
```
```  2625 end
```