src/HOL/IntDiv.thy
author wenzelm
Wed Sep 17 21:27:14 2008 +0200 (2008-09-17)
changeset 28263 69eaa97e7e96
parent 28262 aa7ca36d67fd
child 28562 4e74209f113e
permissions -rw-r--r--
moved global ML bindings to global place;
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(*  Title:      HOL/IntDiv.thy
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    ID:         $Id$
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    Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
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    Copyright   1999  University of Cambridge
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*)
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header{*The Division Operators div and mod; the Divides Relation dvd*}
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theory IntDiv
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imports Int Divides FunDef
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begin
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constdefs
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  quorem :: "(int*int) * (int*int) => bool"
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    --{*definition of quotient and remainder*}
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    [code func]: "quorem == %((a,b), (q,r)).
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                      a = b*q + r &
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                      (if 0 < b then 0\<le>r & r<b else b<r & r \<le> 0)"
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  adjust :: "[int, int*int] => int*int"
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    --{*for the division algorithm*}
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    [code func]: "adjust b == %(q,r). if 0 \<le> r-b then (2*q + 1, r-b)
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                         else (2*q, r)"
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text{*algorithm for the case @{text "a\<ge>0, b>0"}*}
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function
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  posDivAlg :: "int \<Rightarrow> int \<Rightarrow> int \<times> int"
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where
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  "posDivAlg a b =
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     (if (a<b | b\<le>0) then (0,a)
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        else adjust b (posDivAlg a (2*b)))"
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by auto
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termination by (relation "measure (%(a,b). nat(a - b + 1))") auto
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text{*algorithm for the case @{text "a<0, b>0"}*}
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function
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  negDivAlg :: "int \<Rightarrow> int \<Rightarrow> int \<times> int"
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where
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  "negDivAlg a b  =
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     (if (0\<le>a+b | b\<le>0) then (-1,a+b)
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      else adjust b (negDivAlg a (2*b)))"
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by auto
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termination by (relation "measure (%(a,b). nat(- a - b))") auto
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text{*algorithm for the general case @{term "b\<noteq>0"}*}
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constdefs
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  negateSnd :: "int*int => int*int"
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    [code func]: "negateSnd == %(q,r). (q,-r)"
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definition
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  divAlg :: "int \<times> int \<Rightarrow> int \<times> int"
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    --{*The full division algorithm considers all possible signs for a, b
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       including the special case @{text "a=0, b<0"} because 
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       @{term negDivAlg} requires @{term "a<0"}.*}
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where
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  "divAlg = (\<lambda>(a, b). (if 0\<le>a then
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                  if 0\<le>b then posDivAlg a b
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                  else if a=0 then (0, 0)
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                       else negateSnd (negDivAlg (-a) (-b))
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               else 
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                  if 0<b then negDivAlg a b
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                  else negateSnd (posDivAlg (-a) (-b))))"
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instantiation int :: Divides.div
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begin
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definition
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  div_def: "a div b = fst (divAlg (a, b))"
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definition
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  mod_def: "a mod b = snd (divAlg (a, b))"
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instance ..
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end
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lemma divAlg_mod_div:
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  "divAlg (p, q) = (p div q, p mod q)"
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  by (auto simp add: div_def mod_def)
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text{*
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Here is the division algorithm in ML:
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\begin{verbatim}
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    fun posDivAlg (a,b) =
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      if a<b then (0,a)
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      else let val (q,r) = posDivAlg(a, 2*b)
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	       in  if 0\<le>r-b then (2*q+1, r-b) else (2*q, r)
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	   end
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    fun negDivAlg (a,b) =
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      if 0\<le>a+b then (~1,a+b)
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      else let val (q,r) = negDivAlg(a, 2*b)
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	       in  if 0\<le>r-b then (2*q+1, r-b) else (2*q, r)
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	   end;
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    fun negateSnd (q,r:int) = (q,~r);
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    fun divAlg (a,b) = if 0\<le>a then 
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			  if b>0 then posDivAlg (a,b) 
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			   else if a=0 then (0,0)
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				else negateSnd (negDivAlg (~a,~b))
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		       else 
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			  if 0<b then negDivAlg (a,b)
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			  else        negateSnd (posDivAlg (~a,~b));
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\end{verbatim}
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*}
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subsection{*Uniqueness and Monotonicity of Quotients and Remainders*}
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lemma unique_quotient_lemma:
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     "[| b*q' + r'  \<le> b*q + r;  0 \<le> r';  r' < b;  r < b |]  
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      ==> q' \<le> (q::int)"
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apply (subgoal_tac "r' + b * (q'-q) \<le> r")
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 prefer 2 apply (simp add: right_diff_distrib)
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apply (subgoal_tac "0 < b * (1 + q - q') ")
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apply (erule_tac [2] order_le_less_trans)
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 prefer 2 apply (simp add: right_diff_distrib right_distrib)
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apply (subgoal_tac "b * q' < b * (1 + q) ")
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 prefer 2 apply (simp add: right_diff_distrib right_distrib)
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apply (simp add: mult_less_cancel_left)
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done
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lemma unique_quotient_lemma_neg:
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     "[| b*q' + r' \<le> b*q + r;  r \<le> 0;  b < r;  b < r' |]  
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      ==> q \<le> (q'::int)"
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by (rule_tac b = "-b" and r = "-r'" and r' = "-r" in unique_quotient_lemma, 
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    auto)
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lemma unique_quotient:
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     "[| quorem ((a,b), (q,r));  quorem ((a,b), (q',r'));  b \<noteq> 0 |]  
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      ==> q = q'"
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apply (simp add: quorem_def linorder_neq_iff split: split_if_asm)
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apply (blast intro: order_antisym
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             dest: order_eq_refl [THEN unique_quotient_lemma] 
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             order_eq_refl [THEN unique_quotient_lemma_neg] sym)+
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done
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lemma unique_remainder:
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     "[| quorem ((a,b), (q,r));  quorem ((a,b), (q',r'));  b \<noteq> 0 |]  
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      ==> r = r'"
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apply (subgoal_tac "q = q'")
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 apply (simp add: quorem_def)
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apply (blast intro: unique_quotient)
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done
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subsection{*Correctness of @{term posDivAlg}, the Algorithm for Non-Negative Dividends*}
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text{*And positive divisors*}
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lemma adjust_eq [simp]:
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     "adjust b (q,r) = 
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      (let diff = r-b in  
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	if 0 \<le> diff then (2*q + 1, diff)   
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                     else (2*q, r))"
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by (simp add: Let_def adjust_def)
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declare posDivAlg.simps [simp del]
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text{*use with a simproc to avoid repeatedly proving the premise*}
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lemma posDivAlg_eqn:
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     "0 < b ==>  
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      posDivAlg a b = (if a<b then (0,a) else adjust b (posDivAlg a (2*b)))"
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by (rule posDivAlg.simps [THEN trans], simp)
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text{*Correctness of @{term posDivAlg}: it computes quotients correctly*}
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theorem posDivAlg_correct:
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  assumes "0 \<le> a" and "0 < b"
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  shows "quorem ((a, b), posDivAlg a b)"
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using prems apply (induct a b rule: posDivAlg.induct)
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apply auto
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apply (simp add: quorem_def)
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apply (subst posDivAlg_eqn, simp add: right_distrib)
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apply (case_tac "a < b")
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apply simp_all
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apply (erule splitE)
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apply (auto simp add: right_distrib Let_def)
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done
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subsection{*Correctness of @{term negDivAlg}, the Algorithm for Negative Dividends*}
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text{*And positive divisors*}
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declare negDivAlg.simps [simp del]
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text{*use with a simproc to avoid repeatedly proving the premise*}
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lemma negDivAlg_eqn:
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     "0 < b ==>  
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      negDivAlg a b =       
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       (if 0\<le>a+b then (-1,a+b) else adjust b (negDivAlg a (2*b)))"
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by (rule negDivAlg.simps [THEN trans], simp)
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(*Correctness of negDivAlg: it computes quotients correctly
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  It doesn't work if a=0 because the 0/b equals 0, not -1*)
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lemma negDivAlg_correct:
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  assumes "a < 0" and "b > 0"
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  shows "quorem ((a, b), negDivAlg a b)"
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using prems apply (induct a b rule: negDivAlg.induct)
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apply (auto simp add: linorder_not_le)
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apply (simp add: quorem_def)
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apply (subst negDivAlg_eqn, assumption)
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apply (case_tac "a + b < (0\<Colon>int)")
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apply simp_all
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apply (erule splitE)
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apply (auto simp add: right_distrib Let_def)
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done
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subsection{*Existence Shown by Proving the Division Algorithm to be Correct*}
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(*the case a=0*)
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lemma quorem_0: "b \<noteq> 0 ==> quorem ((0,b), (0,0))"
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by (auto simp add: quorem_def linorder_neq_iff)
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lemma posDivAlg_0 [simp]: "posDivAlg 0 b = (0, 0)"
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by (subst posDivAlg.simps, auto)
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lemma negDivAlg_minus1 [simp]: "negDivAlg -1 b = (-1, b - 1)"
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by (subst negDivAlg.simps, auto)
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lemma negateSnd_eq [simp]: "negateSnd(q,r) = (q,-r)"
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by (simp add: negateSnd_def)
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lemma quorem_neg: "quorem ((-a,-b), qr) ==> quorem ((a,b), negateSnd qr)"
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by (auto simp add: split_ifs quorem_def)
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lemma divAlg_correct: "b \<noteq> 0 ==> quorem ((a,b), divAlg (a, b))"
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by (force simp add: linorder_neq_iff quorem_0 divAlg_def quorem_neg
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                    posDivAlg_correct negDivAlg_correct)
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text{*Arbitrary definitions for division by zero.  Useful to simplify 
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    certain equations.*}
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lemma DIVISION_BY_ZERO [simp]: "a div (0::int) = 0 & a mod (0::int) = a"
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by (simp add: div_def mod_def divAlg_def posDivAlg.simps)  
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text{*Basic laws about division and remainder*}
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lemma zmod_zdiv_equality: "(a::int) = b * (a div b) + (a mod b)"
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apply (case_tac "b = 0", simp)
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apply (cut_tac a = a and b = b in divAlg_correct)
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apply (auto simp add: quorem_def div_def mod_def)
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done
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lemma zdiv_zmod_equality: "(b * (a div b) + (a mod b)) + k = (a::int)+k"
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by(simp add: zmod_zdiv_equality[symmetric])
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lemma zdiv_zmod_equality2: "((a div b) * b + (a mod b)) + k = (a::int)+k"
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by(simp add: mult_commute zmod_zdiv_equality[symmetric])
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text {* Tool setup *}
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ML {*
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local 
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structure CancelDivMod = CancelDivModFun(
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struct
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  val div_name = @{const_name Divides.div};
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  val mod_name = @{const_name Divides.mod};
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  val mk_binop = HOLogic.mk_binop;
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  val mk_sum = Int_Numeral_Simprocs.mk_sum HOLogic.intT;
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  val dest_sum = Int_Numeral_Simprocs.dest_sum;
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  val div_mod_eqs =
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    map mk_meta_eq [@{thm zdiv_zmod_equality},
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      @{thm zdiv_zmod_equality2}];
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  val trans = trans;
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  val prove_eq_sums =
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    let
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      val simps = @{thm diff_int_def} :: Int_Numeral_Simprocs.add_0s @ @{thms zadd_ac}
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    in ArithData.prove_conv all_tac (ArithData.simp_all_tac simps) end;
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end)
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in
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val cancel_zdiv_zmod_proc = Simplifier.simproc (the_context ())
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  "cancel_zdiv_zmod" ["(m::int) + n"] (K CancelDivMod.proc)
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end;
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Addsimprocs [cancel_zdiv_zmod_proc]
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*}
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lemma pos_mod_conj : "(0::int) < b ==> 0 \<le> a mod b & a mod b < b"
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apply (cut_tac a = a and b = b in divAlg_correct)
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apply (auto simp add: quorem_def mod_def)
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done
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lemmas pos_mod_sign  [simp] = pos_mod_conj [THEN conjunct1, standard]
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   and pos_mod_bound [simp] = pos_mod_conj [THEN conjunct2, standard]
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lemma neg_mod_conj : "b < (0::int) ==> a mod b \<le> 0 & b < a mod b"
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apply (cut_tac a = a and b = b in divAlg_correct)
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apply (auto simp add: quorem_def div_def mod_def)
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done
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lemmas neg_mod_sign  [simp] = neg_mod_conj [THEN conjunct1, standard]
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   and neg_mod_bound [simp] = neg_mod_conj [THEN conjunct2, standard]
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subsection{*General Properties of div and mod*}
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lemma quorem_div_mod: "b \<noteq> 0 ==> quorem ((a, b), (a div b, a mod b))"
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apply (cut_tac a = a and b = b in zmod_zdiv_equality)
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apply (force simp add: quorem_def linorder_neq_iff)
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done
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lemma quorem_div: "[| quorem((a,b),(q,r));  b \<noteq> 0 |] ==> a div b = q"
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by (simp add: quorem_div_mod [THEN unique_quotient])
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lemma quorem_mod: "[| quorem((a,b),(q,r));  b \<noteq> 0 |] ==> a mod b = r"
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by (simp add: quorem_div_mod [THEN unique_remainder])
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lemma div_pos_pos_trivial: "[| (0::int) \<le> a;  a < b |] ==> a div b = 0"
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apply (rule quorem_div)
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apply (auto simp add: quorem_def)
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   324
done
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   325
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   326
lemma div_neg_neg_trivial: "[| a \<le> (0::int);  b < a |] ==> a div b = 0"
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   327
apply (rule quorem_div)
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   328
apply (auto simp add: quorem_def)
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   329
done
wenzelm@23164
   330
wenzelm@23164
   331
lemma div_pos_neg_trivial: "[| (0::int) < a;  a+b \<le> 0 |] ==> a div b = -1"
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   332
apply (rule quorem_div)
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   333
apply (auto simp add: quorem_def)
wenzelm@23164
   334
done
wenzelm@23164
   335
wenzelm@23164
   336
(*There is no div_neg_pos_trivial because  0 div b = 0 would supersede it*)
wenzelm@23164
   337
wenzelm@23164
   338
lemma mod_pos_pos_trivial: "[| (0::int) \<le> a;  a < b |] ==> a mod b = a"
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   339
apply (rule_tac q = 0 in quorem_mod)
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   340
apply (auto simp add: quorem_def)
wenzelm@23164
   341
done
wenzelm@23164
   342
wenzelm@23164
   343
lemma mod_neg_neg_trivial: "[| a \<le> (0::int);  b < a |] ==> a mod b = a"
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   344
apply (rule_tac q = 0 in quorem_mod)
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   345
apply (auto simp add: quorem_def)
wenzelm@23164
   346
done
wenzelm@23164
   347
wenzelm@23164
   348
lemma mod_pos_neg_trivial: "[| (0::int) < a;  a+b \<le> 0 |] ==> a mod b = a+b"
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   349
apply (rule_tac q = "-1" in quorem_mod)
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   350
apply (auto simp add: quorem_def)
wenzelm@23164
   351
done
wenzelm@23164
   352
wenzelm@23164
   353
text{*There is no @{text mod_neg_pos_trivial}.*}
wenzelm@23164
   354
wenzelm@23164
   355
wenzelm@23164
   356
(*Simpler laws such as -a div b = -(a div b) FAIL, but see just below*)
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   357
lemma zdiv_zminus_zminus [simp]: "(-a) div (-b) = a div (b::int)"
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   358
apply (case_tac "b = 0", simp)
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   359
apply (simp add: quorem_div_mod [THEN quorem_neg, simplified, 
wenzelm@23164
   360
                                 THEN quorem_div, THEN sym])
wenzelm@23164
   361
wenzelm@23164
   362
done
wenzelm@23164
   363
wenzelm@23164
   364
(*Simpler laws such as -a mod b = -(a mod b) FAIL, but see just below*)
wenzelm@23164
   365
lemma zmod_zminus_zminus [simp]: "(-a) mod (-b) = - (a mod (b::int))"
wenzelm@23164
   366
apply (case_tac "b = 0", simp)
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   367
apply (subst quorem_div_mod [THEN quorem_neg, simplified, THEN quorem_mod],
wenzelm@23164
   368
       auto)
wenzelm@23164
   369
done
wenzelm@23164
   370
wenzelm@23164
   371
wenzelm@23164
   372
subsection{*Laws for div and mod with Unary Minus*}
wenzelm@23164
   373
wenzelm@23164
   374
lemma zminus1_lemma:
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   375
     "quorem((a,b),(q,r))  
wenzelm@23164
   376
      ==> quorem ((-a,b), (if r=0 then -q else -q - 1),  
wenzelm@23164
   377
                          (if r=0 then 0 else b-r))"
wenzelm@23164
   378
by (force simp add: split_ifs quorem_def linorder_neq_iff right_diff_distrib)
wenzelm@23164
   379
wenzelm@23164
   380
wenzelm@23164
   381
lemma zdiv_zminus1_eq_if:
wenzelm@23164
   382
     "b \<noteq> (0::int)  
wenzelm@23164
   383
      ==> (-a) div b =  
wenzelm@23164
   384
          (if a mod b = 0 then - (a div b) else  - (a div b) - 1)"
wenzelm@23164
   385
by (blast intro: quorem_div_mod [THEN zminus1_lemma, THEN quorem_div])
wenzelm@23164
   386
wenzelm@23164
   387
lemma zmod_zminus1_eq_if:
wenzelm@23164
   388
     "(-a::int) mod b = (if a mod b = 0 then 0 else  b - (a mod b))"
wenzelm@23164
   389
apply (case_tac "b = 0", simp)
wenzelm@23164
   390
apply (blast intro: quorem_div_mod [THEN zminus1_lemma, THEN quorem_mod])
wenzelm@23164
   391
done
wenzelm@23164
   392
wenzelm@23164
   393
lemma zdiv_zminus2: "a div (-b) = (-a::int) div b"
wenzelm@23164
   394
by (cut_tac a = "-a" in zdiv_zminus_zminus, auto)
wenzelm@23164
   395
wenzelm@23164
   396
lemma zmod_zminus2: "a mod (-b) = - ((-a::int) mod b)"
wenzelm@23164
   397
by (cut_tac a = "-a" and b = b in zmod_zminus_zminus, auto)
wenzelm@23164
   398
wenzelm@23164
   399
lemma zdiv_zminus2_eq_if:
wenzelm@23164
   400
     "b \<noteq> (0::int)  
wenzelm@23164
   401
      ==> a div (-b) =  
wenzelm@23164
   402
          (if a mod b = 0 then - (a div b) else  - (a div b) - 1)"
wenzelm@23164
   403
by (simp add: zdiv_zminus1_eq_if zdiv_zminus2)
wenzelm@23164
   404
wenzelm@23164
   405
lemma zmod_zminus2_eq_if:
wenzelm@23164
   406
     "a mod (-b::int) = (if a mod b = 0 then 0 else  (a mod b) - b)"
wenzelm@23164
   407
by (simp add: zmod_zminus1_eq_if zmod_zminus2)
wenzelm@23164
   408
wenzelm@23164
   409
wenzelm@23164
   410
subsection{*Division of a Number by Itself*}
wenzelm@23164
   411
wenzelm@23164
   412
lemma self_quotient_aux1: "[| (0::int) < a; a = r + a*q; r < a |] ==> 1 \<le> q"
wenzelm@23164
   413
apply (subgoal_tac "0 < a*q")
wenzelm@23164
   414
 apply (simp add: zero_less_mult_iff, arith)
wenzelm@23164
   415
done
wenzelm@23164
   416
wenzelm@23164
   417
lemma self_quotient_aux2: "[| (0::int) < a; a = r + a*q; 0 \<le> r |] ==> q \<le> 1"
wenzelm@23164
   418
apply (subgoal_tac "0 \<le> a* (1-q) ")
wenzelm@23164
   419
 apply (simp add: zero_le_mult_iff)
wenzelm@23164
   420
apply (simp add: right_diff_distrib)
wenzelm@23164
   421
done
wenzelm@23164
   422
wenzelm@23164
   423
lemma self_quotient: "[| quorem((a,a),(q,r));  a \<noteq> (0::int) |] ==> q = 1"
wenzelm@23164
   424
apply (simp add: split_ifs quorem_def linorder_neq_iff)
wenzelm@23164
   425
apply (rule order_antisym, safe, simp_all)
wenzelm@23164
   426
apply (rule_tac [3] a = "-a" and r = "-r" in self_quotient_aux1)
wenzelm@23164
   427
apply (rule_tac a = "-a" and r = "-r" in self_quotient_aux2)
wenzelm@23164
   428
apply (force intro: self_quotient_aux1 self_quotient_aux2 simp add: add_commute)+
wenzelm@23164
   429
done
wenzelm@23164
   430
wenzelm@23164
   431
lemma self_remainder: "[| quorem((a,a),(q,r));  a \<noteq> (0::int) |] ==> r = 0"
wenzelm@23164
   432
apply (frule self_quotient, assumption)
wenzelm@23164
   433
apply (simp add: quorem_def)
wenzelm@23164
   434
done
wenzelm@23164
   435
wenzelm@23164
   436
lemma zdiv_self [simp]: "a \<noteq> 0 ==> a div a = (1::int)"
wenzelm@23164
   437
by (simp add: quorem_div_mod [THEN self_quotient])
wenzelm@23164
   438
wenzelm@23164
   439
(*Here we have 0 mod 0 = 0, also assumed by Knuth (who puts m mod 0 = 0) *)
wenzelm@23164
   440
lemma zmod_self [simp]: "a mod a = (0::int)"
wenzelm@23164
   441
apply (case_tac "a = 0", simp)
wenzelm@23164
   442
apply (simp add: quorem_div_mod [THEN self_remainder])
wenzelm@23164
   443
done
wenzelm@23164
   444
wenzelm@23164
   445
wenzelm@23164
   446
subsection{*Computation of Division and Remainder*}
wenzelm@23164
   447
wenzelm@23164
   448
lemma zdiv_zero [simp]: "(0::int) div b = 0"
wenzelm@23164
   449
by (simp add: div_def divAlg_def)
wenzelm@23164
   450
wenzelm@23164
   451
lemma div_eq_minus1: "(0::int) < b ==> -1 div b = -1"
wenzelm@23164
   452
by (simp add: div_def divAlg_def)
wenzelm@23164
   453
wenzelm@23164
   454
lemma zmod_zero [simp]: "(0::int) mod b = 0"
wenzelm@23164
   455
by (simp add: mod_def divAlg_def)
wenzelm@23164
   456
wenzelm@23164
   457
lemma zdiv_minus1: "(0::int) < b ==> -1 div b = -1"
wenzelm@23164
   458
by (simp add: div_def divAlg_def)
wenzelm@23164
   459
wenzelm@23164
   460
lemma zmod_minus1: "(0::int) < b ==> -1 mod b = b - 1"
wenzelm@23164
   461
by (simp add: mod_def divAlg_def)
wenzelm@23164
   462
wenzelm@23164
   463
text{*a positive, b positive *}
wenzelm@23164
   464
wenzelm@23164
   465
lemma div_pos_pos: "[| 0 < a;  0 \<le> b |] ==> a div b = fst (posDivAlg a b)"
wenzelm@23164
   466
by (simp add: div_def divAlg_def)
wenzelm@23164
   467
wenzelm@23164
   468
lemma mod_pos_pos: "[| 0 < a;  0 \<le> b |] ==> a mod b = snd (posDivAlg a b)"
wenzelm@23164
   469
by (simp add: mod_def divAlg_def)
wenzelm@23164
   470
wenzelm@23164
   471
text{*a negative, b positive *}
wenzelm@23164
   472
wenzelm@23164
   473
lemma div_neg_pos: "[| a < 0;  0 < b |] ==> a div b = fst (negDivAlg a b)"
wenzelm@23164
   474
by (simp add: div_def divAlg_def)
wenzelm@23164
   475
wenzelm@23164
   476
lemma mod_neg_pos: "[| a < 0;  0 < b |] ==> a mod b = snd (negDivAlg a b)"
wenzelm@23164
   477
by (simp add: mod_def divAlg_def)
wenzelm@23164
   478
wenzelm@23164
   479
text{*a positive, b negative *}
wenzelm@23164
   480
wenzelm@23164
   481
lemma div_pos_neg:
wenzelm@23164
   482
     "[| 0 < a;  b < 0 |] ==> a div b = fst (negateSnd (negDivAlg (-a) (-b)))"
wenzelm@23164
   483
by (simp add: div_def divAlg_def)
wenzelm@23164
   484
wenzelm@23164
   485
lemma mod_pos_neg:
wenzelm@23164
   486
     "[| 0 < a;  b < 0 |] ==> a mod b = snd (negateSnd (negDivAlg (-a) (-b)))"
wenzelm@23164
   487
by (simp add: mod_def divAlg_def)
wenzelm@23164
   488
wenzelm@23164
   489
text{*a negative, b negative *}
wenzelm@23164
   490
wenzelm@23164
   491
lemma div_neg_neg:
wenzelm@23164
   492
     "[| a < 0;  b \<le> 0 |] ==> a div b = fst (negateSnd (posDivAlg (-a) (-b)))"
wenzelm@23164
   493
by (simp add: div_def divAlg_def)
wenzelm@23164
   494
wenzelm@23164
   495
lemma mod_neg_neg:
wenzelm@23164
   496
     "[| a < 0;  b \<le> 0 |] ==> a mod b = snd (negateSnd (posDivAlg (-a) (-b)))"
wenzelm@23164
   497
by (simp add: mod_def divAlg_def)
wenzelm@23164
   498
wenzelm@23164
   499
text {*Simplify expresions in which div and mod combine numerical constants*}
wenzelm@23164
   500
huffman@24481
   501
lemma quoremI:
huffman@24481
   502
  "\<lbrakk>a == b * q + r; if 0 < b then 0 \<le> r \<and> r < b else b < r \<and> r \<le> 0\<rbrakk>
huffman@24481
   503
    \<Longrightarrow> quorem ((a, b), (q, r))"
huffman@24481
   504
  unfolding quorem_def by simp
huffman@24481
   505
huffman@24481
   506
lemmas quorem_div_eq = quoremI [THEN quorem_div, THEN eq_reflection]
huffman@24481
   507
lemmas quorem_mod_eq = quoremI [THEN quorem_mod, THEN eq_reflection]
huffman@24481
   508
lemmas arithmetic_simps =
huffman@24481
   509
  arith_simps
huffman@24481
   510
  add_special
huffman@24481
   511
  OrderedGroup.add_0_left
huffman@24481
   512
  OrderedGroup.add_0_right
huffman@24481
   513
  mult_zero_left
huffman@24481
   514
  mult_zero_right
huffman@24481
   515
  mult_1_left
huffman@24481
   516
  mult_1_right
huffman@24481
   517
huffman@24481
   518
(* simprocs adapted from HOL/ex/Binary.thy *)
huffman@24481
   519
ML {*
huffman@24481
   520
local
huffman@24481
   521
  infix ==;
huffman@24481
   522
  val op == = Logic.mk_equals;
huffman@24481
   523
  fun plus m n = @{term "plus :: int \<Rightarrow> int \<Rightarrow> int"} $ m $ n;
huffman@24481
   524
  fun mult m n = @{term "times :: int \<Rightarrow> int \<Rightarrow> int"} $ m $ n;
huffman@24481
   525
huffman@24481
   526
  val binary_ss = HOL_basic_ss addsimps @{thms arithmetic_simps};
huffman@24481
   527
  fun prove ctxt prop =
huffman@24481
   528
    Goal.prove ctxt [] [] prop (fn _ => ALLGOALS (full_simp_tac binary_ss));
huffman@24481
   529
huffman@24481
   530
  fun binary_proc proc ss ct =
huffman@24481
   531
    (case Thm.term_of ct of
huffman@24481
   532
      _ $ t $ u =>
huffman@24481
   533
      (case try (pairself (`(snd o HOLogic.dest_number))) (t, u) of
huffman@24481
   534
        SOME args => proc (Simplifier.the_context ss) args
huffman@24481
   535
      | NONE => NONE)
huffman@24481
   536
    | _ => NONE);
huffman@24481
   537
in
huffman@24481
   538
huffman@24481
   539
fun divmod_proc rule = binary_proc (fn ctxt => fn ((m, t), (n, u)) =>
huffman@24481
   540
  if n = 0 then NONE
huffman@24481
   541
  else
wenzelm@24630
   542
    let val (k, l) = Integer.div_mod m n;
huffman@24481
   543
        fun mk_num x = HOLogic.mk_number HOLogic.intT x;
huffman@24481
   544
    in SOME (rule OF [prove ctxt (t == plus (mult u (mk_num k)) (mk_num l))])
huffman@24481
   545
    end);
huffman@24481
   546
huffman@24481
   547
end;
huffman@24481
   548
*}
huffman@24481
   549
huffman@24481
   550
simproc_setup binary_int_div ("number_of m div number_of n :: int") =
huffman@24481
   551
  {* K (divmod_proc (@{thm quorem_div_eq})) *}
huffman@24481
   552
huffman@24481
   553
simproc_setup binary_int_mod ("number_of m mod number_of n :: int") =
huffman@24481
   554
  {* K (divmod_proc (@{thm quorem_mod_eq})) *}
huffman@24481
   555
huffman@24481
   556
(* The following 8 lemmas are made unnecessary by the above simprocs: *)
huffman@24481
   557
huffman@24481
   558
lemmas div_pos_pos_number_of =
wenzelm@23164
   559
    div_pos_pos [of "number_of v" "number_of w", standard]
wenzelm@23164
   560
huffman@24481
   561
lemmas div_neg_pos_number_of =
wenzelm@23164
   562
    div_neg_pos [of "number_of v" "number_of w", standard]
wenzelm@23164
   563
huffman@24481
   564
lemmas div_pos_neg_number_of =
wenzelm@23164
   565
    div_pos_neg [of "number_of v" "number_of w", standard]
wenzelm@23164
   566
huffman@24481
   567
lemmas div_neg_neg_number_of =
wenzelm@23164
   568
    div_neg_neg [of "number_of v" "number_of w", standard]
wenzelm@23164
   569
wenzelm@23164
   570
huffman@24481
   571
lemmas mod_pos_pos_number_of =
wenzelm@23164
   572
    mod_pos_pos [of "number_of v" "number_of w", standard]
wenzelm@23164
   573
huffman@24481
   574
lemmas mod_neg_pos_number_of =
wenzelm@23164
   575
    mod_neg_pos [of "number_of v" "number_of w", standard]
wenzelm@23164
   576
huffman@24481
   577
lemmas mod_pos_neg_number_of =
wenzelm@23164
   578
    mod_pos_neg [of "number_of v" "number_of w", standard]
wenzelm@23164
   579
huffman@24481
   580
lemmas mod_neg_neg_number_of =
wenzelm@23164
   581
    mod_neg_neg [of "number_of v" "number_of w", standard]
wenzelm@23164
   582
wenzelm@23164
   583
wenzelm@23164
   584
lemmas posDivAlg_eqn_number_of [simp] =
wenzelm@23164
   585
    posDivAlg_eqn [of "number_of v" "number_of w", standard]
wenzelm@23164
   586
wenzelm@23164
   587
lemmas negDivAlg_eqn_number_of [simp] =
wenzelm@23164
   588
    negDivAlg_eqn [of "number_of v" "number_of w", standard]
wenzelm@23164
   589
wenzelm@23164
   590
wenzelm@23164
   591
text{*Special-case simplification *}
wenzelm@23164
   592
wenzelm@23164
   593
lemma zmod_1 [simp]: "a mod (1::int) = 0"
wenzelm@23164
   594
apply (cut_tac a = a and b = 1 in pos_mod_sign)
wenzelm@23164
   595
apply (cut_tac [2] a = a and b = 1 in pos_mod_bound)
wenzelm@23164
   596
apply (auto simp del:pos_mod_bound pos_mod_sign)
wenzelm@23164
   597
done
wenzelm@23164
   598
wenzelm@23164
   599
lemma zdiv_1 [simp]: "a div (1::int) = a"
wenzelm@23164
   600
by (cut_tac a = a and b = 1 in zmod_zdiv_equality, auto)
wenzelm@23164
   601
wenzelm@23164
   602
lemma zmod_minus1_right [simp]: "a mod (-1::int) = 0"
wenzelm@23164
   603
apply (cut_tac a = a and b = "-1" in neg_mod_sign)
wenzelm@23164
   604
apply (cut_tac [2] a = a and b = "-1" in neg_mod_bound)
wenzelm@23164
   605
apply (auto simp del: neg_mod_sign neg_mod_bound)
wenzelm@23164
   606
done
wenzelm@23164
   607
wenzelm@23164
   608
lemma zdiv_minus1_right [simp]: "a div (-1::int) = -a"
wenzelm@23164
   609
by (cut_tac a = a and b = "-1" in zmod_zdiv_equality, auto)
wenzelm@23164
   610
wenzelm@23164
   611
(** The last remaining special cases for constant arithmetic:
wenzelm@23164
   612
    1 div z and 1 mod z **)
wenzelm@23164
   613
wenzelm@23164
   614
lemmas div_pos_pos_1_number_of [simp] =
wenzelm@23164
   615
    div_pos_pos [OF int_0_less_1, of "number_of w", standard]
wenzelm@23164
   616
wenzelm@23164
   617
lemmas div_pos_neg_1_number_of [simp] =
wenzelm@23164
   618
    div_pos_neg [OF int_0_less_1, of "number_of w", standard]
wenzelm@23164
   619
wenzelm@23164
   620
lemmas mod_pos_pos_1_number_of [simp] =
wenzelm@23164
   621
    mod_pos_pos [OF int_0_less_1, of "number_of w", standard]
wenzelm@23164
   622
wenzelm@23164
   623
lemmas mod_pos_neg_1_number_of [simp] =
wenzelm@23164
   624
    mod_pos_neg [OF int_0_less_1, of "number_of w", standard]
wenzelm@23164
   625
wenzelm@23164
   626
wenzelm@23164
   627
lemmas posDivAlg_eqn_1_number_of [simp] =
wenzelm@23164
   628
    posDivAlg_eqn [of concl: 1 "number_of w", standard]
wenzelm@23164
   629
wenzelm@23164
   630
lemmas negDivAlg_eqn_1_number_of [simp] =
wenzelm@23164
   631
    negDivAlg_eqn [of concl: 1 "number_of w", standard]
wenzelm@23164
   632
wenzelm@23164
   633
wenzelm@23164
   634
wenzelm@23164
   635
subsection{*Monotonicity in the First Argument (Dividend)*}
wenzelm@23164
   636
wenzelm@23164
   637
lemma zdiv_mono1: "[| a \<le> a';  0 < (b::int) |] ==> a div b \<le> a' div b"
wenzelm@23164
   638
apply (cut_tac a = a and b = b in zmod_zdiv_equality)
wenzelm@23164
   639
apply (cut_tac a = a' and b = b in zmod_zdiv_equality)
wenzelm@23164
   640
apply (rule unique_quotient_lemma)
wenzelm@23164
   641
apply (erule subst)
wenzelm@23164
   642
apply (erule subst, simp_all)
wenzelm@23164
   643
done
wenzelm@23164
   644
wenzelm@23164
   645
lemma zdiv_mono1_neg: "[| a \<le> a';  (b::int) < 0 |] ==> a' div b \<le> a div b"
wenzelm@23164
   646
apply (cut_tac a = a and b = b in zmod_zdiv_equality)
wenzelm@23164
   647
apply (cut_tac a = a' and b = b in zmod_zdiv_equality)
wenzelm@23164
   648
apply (rule unique_quotient_lemma_neg)
wenzelm@23164
   649
apply (erule subst)
wenzelm@23164
   650
apply (erule subst, simp_all)
wenzelm@23164
   651
done
wenzelm@23164
   652
wenzelm@23164
   653
wenzelm@23164
   654
subsection{*Monotonicity in the Second Argument (Divisor)*}
wenzelm@23164
   655
wenzelm@23164
   656
lemma q_pos_lemma:
wenzelm@23164
   657
     "[| 0 \<le> b'*q' + r'; r' < b';  0 < b' |] ==> 0 \<le> (q'::int)"
wenzelm@23164
   658
apply (subgoal_tac "0 < b'* (q' + 1) ")
wenzelm@23164
   659
 apply (simp add: zero_less_mult_iff)
wenzelm@23164
   660
apply (simp add: right_distrib)
wenzelm@23164
   661
done
wenzelm@23164
   662
wenzelm@23164
   663
lemma zdiv_mono2_lemma:
wenzelm@23164
   664
     "[| b*q + r = b'*q' + r';  0 \<le> b'*q' + r';   
wenzelm@23164
   665
         r' < b';  0 \<le> r;  0 < b';  b' \<le> b |]   
wenzelm@23164
   666
      ==> q \<le> (q'::int)"
wenzelm@23164
   667
apply (frule q_pos_lemma, assumption+) 
wenzelm@23164
   668
apply (subgoal_tac "b*q < b* (q' + 1) ")
wenzelm@23164
   669
 apply (simp add: mult_less_cancel_left)
wenzelm@23164
   670
apply (subgoal_tac "b*q = r' - r + b'*q'")
wenzelm@23164
   671
 prefer 2 apply simp
wenzelm@23164
   672
apply (simp (no_asm_simp) add: right_distrib)
wenzelm@23164
   673
apply (subst add_commute, rule zadd_zless_mono, arith)
wenzelm@23164
   674
apply (rule mult_right_mono, auto)
wenzelm@23164
   675
done
wenzelm@23164
   676
wenzelm@23164
   677
lemma zdiv_mono2:
wenzelm@23164
   678
     "[| (0::int) \<le> a;  0 < b';  b' \<le> b |] ==> a div b \<le> a div b'"
wenzelm@23164
   679
apply (subgoal_tac "b \<noteq> 0")
wenzelm@23164
   680
 prefer 2 apply arith
wenzelm@23164
   681
apply (cut_tac a = a and b = b in zmod_zdiv_equality)
wenzelm@23164
   682
apply (cut_tac a = a and b = b' in zmod_zdiv_equality)
wenzelm@23164
   683
apply (rule zdiv_mono2_lemma)
wenzelm@23164
   684
apply (erule subst)
wenzelm@23164
   685
apply (erule subst, simp_all)
wenzelm@23164
   686
done
wenzelm@23164
   687
wenzelm@23164
   688
lemma q_neg_lemma:
wenzelm@23164
   689
     "[| b'*q' + r' < 0;  0 \<le> r';  0 < b' |] ==> q' \<le> (0::int)"
wenzelm@23164
   690
apply (subgoal_tac "b'*q' < 0")
wenzelm@23164
   691
 apply (simp add: mult_less_0_iff, arith)
wenzelm@23164
   692
done
wenzelm@23164
   693
wenzelm@23164
   694
lemma zdiv_mono2_neg_lemma:
wenzelm@23164
   695
     "[| b*q + r = b'*q' + r';  b'*q' + r' < 0;   
wenzelm@23164
   696
         r < b;  0 \<le> r';  0 < b';  b' \<le> b |]   
wenzelm@23164
   697
      ==> q' \<le> (q::int)"
wenzelm@23164
   698
apply (frule q_neg_lemma, assumption+) 
wenzelm@23164
   699
apply (subgoal_tac "b*q' < b* (q + 1) ")
wenzelm@23164
   700
 apply (simp add: mult_less_cancel_left)
wenzelm@23164
   701
apply (simp add: right_distrib)
wenzelm@23164
   702
apply (subgoal_tac "b*q' \<le> b'*q'")
wenzelm@23164
   703
 prefer 2 apply (simp add: mult_right_mono_neg, arith)
wenzelm@23164
   704
done
wenzelm@23164
   705
wenzelm@23164
   706
lemma zdiv_mono2_neg:
wenzelm@23164
   707
     "[| a < (0::int);  0 < b';  b' \<le> b |] ==> a div b' \<le> a div b"
wenzelm@23164
   708
apply (cut_tac a = a and b = b in zmod_zdiv_equality)
wenzelm@23164
   709
apply (cut_tac a = a and b = b' in zmod_zdiv_equality)
wenzelm@23164
   710
apply (rule zdiv_mono2_neg_lemma)
wenzelm@23164
   711
apply (erule subst)
wenzelm@23164
   712
apply (erule subst, simp_all)
wenzelm@23164
   713
done
wenzelm@23164
   714
haftmann@25942
   715
wenzelm@23164
   716
subsection{*More Algebraic Laws for div and mod*}
wenzelm@23164
   717
wenzelm@23164
   718
text{*proving (a*b) div c = a * (b div c) + a * (b mod c) *}
wenzelm@23164
   719
wenzelm@23164
   720
lemma zmult1_lemma:
wenzelm@23164
   721
     "[| quorem((b,c),(q,r));  c \<noteq> 0 |]  
wenzelm@23164
   722
      ==> quorem ((a*b, c), (a*q + a*r div c, a*r mod c))"
wenzelm@23164
   723
by (force simp add: split_ifs quorem_def linorder_neq_iff right_distrib)
wenzelm@23164
   724
wenzelm@23164
   725
lemma zdiv_zmult1_eq: "(a*b) div c = a*(b div c) + a*(b mod c) div (c::int)"
wenzelm@23164
   726
apply (case_tac "c = 0", simp)
wenzelm@23164
   727
apply (blast intro: quorem_div_mod [THEN zmult1_lemma, THEN quorem_div])
wenzelm@23164
   728
done
wenzelm@23164
   729
wenzelm@23164
   730
lemma zmod_zmult1_eq: "(a*b) mod c = a*(b mod c) mod (c::int)"
wenzelm@23164
   731
apply (case_tac "c = 0", simp)
wenzelm@23164
   732
apply (blast intro: quorem_div_mod [THEN zmult1_lemma, THEN quorem_mod])
wenzelm@23164
   733
done
wenzelm@23164
   734
wenzelm@23164
   735
lemma zmod_zmult1_eq': "(a*b) mod (c::int) = ((a mod c) * b) mod c"
wenzelm@23164
   736
apply (rule trans)
wenzelm@23164
   737
apply (rule_tac s = "b*a mod c" in trans)
wenzelm@23164
   738
apply (rule_tac [2] zmod_zmult1_eq)
wenzelm@23164
   739
apply (simp_all add: mult_commute)
wenzelm@23164
   740
done
wenzelm@23164
   741
wenzelm@23164
   742
lemma zmod_zmult_distrib: "(a*b) mod (c::int) = ((a mod c) * (b mod c)) mod c"
wenzelm@23164
   743
apply (rule zmod_zmult1_eq' [THEN trans])
wenzelm@23164
   744
apply (rule zmod_zmult1_eq)
wenzelm@23164
   745
done
wenzelm@23164
   746
wenzelm@23164
   747
lemma zdiv_zmult_self1 [simp]: "b \<noteq> (0::int) ==> (a*b) div b = a"
wenzelm@23164
   748
by (simp add: zdiv_zmult1_eq)
wenzelm@23164
   749
haftmann@27651
   750
lemma mod_div_trivial [simp]: "(a mod b) div b = (0::int)"
haftmann@27651
   751
apply (case_tac "b = 0", simp)
haftmann@27651
   752
apply (auto simp add: linorder_neq_iff div_pos_pos_trivial div_neg_neg_trivial)
haftmann@27651
   753
done
haftmann@27651
   754
haftmann@27651
   755
lemma mod_mod_trivial [simp]: "(a mod b) mod b = a mod (b::int)"
haftmann@27651
   756
apply (case_tac "b = 0", simp)
haftmann@27651
   757
apply (force simp add: linorder_neq_iff mod_pos_pos_trivial mod_neg_neg_trivial)
haftmann@27651
   758
done
haftmann@27651
   759
haftmann@27651
   760
text{*proving (a+b) div c = a div c + b div c + ((a mod c + b mod c) div c) *}
haftmann@27651
   761
haftmann@27651
   762
lemma zadd1_lemma:
haftmann@27651
   763
     "[| quorem((a,c),(aq,ar));  quorem((b,c),(bq,br));  c \<noteq> 0 |]  
haftmann@27651
   764
      ==> quorem ((a+b, c), (aq + bq + (ar+br) div c, (ar+br) mod c))"
haftmann@27651
   765
by (force simp add: split_ifs quorem_def linorder_neq_iff right_distrib)
haftmann@27651
   766
haftmann@27651
   767
(*NOT suitable for rewriting: the RHS has an instance of the LHS*)
haftmann@27651
   768
lemma zdiv_zadd1_eq:
haftmann@27651
   769
     "(a+b) div (c::int) = a div c + b div c + ((a mod c + b mod c) div c)"
haftmann@27651
   770
apply (case_tac "c = 0", simp)
haftmann@27651
   771
apply (blast intro: zadd1_lemma [OF quorem_div_mod quorem_div_mod] quorem_div)
haftmann@27651
   772
done
haftmann@27651
   773
haftmann@27651
   774
lemma zmod_zadd1_eq: "(a+b) mod (c::int) = (a mod c + b mod c) mod c"
haftmann@27651
   775
apply (case_tac "c = 0", simp)
haftmann@27651
   776
apply (blast intro: zadd1_lemma [OF quorem_div_mod quorem_div_mod] quorem_mod)
haftmann@27651
   777
done
haftmann@27651
   778
haftmann@27651
   779
lemma zdiv_zadd_self1[simp]: "a \<noteq> (0::int) ==> (a+b) div a = b div a + 1"
haftmann@27651
   780
by (simp add: zdiv_zadd1_eq)
haftmann@27651
   781
haftmann@27651
   782
lemma zdiv_zadd_self2[simp]: "a \<noteq> (0::int) ==> (b+a) div a = b div a + 1"
haftmann@27651
   783
by (simp add: zdiv_zadd1_eq)
haftmann@27651
   784
haftmann@25942
   785
instance int :: semiring_div
haftmann@27651
   786
proof
haftmann@27651
   787
  fix a b c :: int
haftmann@27651
   788
  assume not0: "b \<noteq> 0"
haftmann@27651
   789
  show "(a + c * b) div b = c + a div b"
haftmann@27651
   790
    unfolding zdiv_zadd1_eq [of a "c * b"] using not0 
haftmann@27651
   791
      by (simp add: zmod_zmult1_eq)
haftmann@27651
   792
qed auto
haftmann@25942
   793
wenzelm@23164
   794
lemma zdiv_zmult_self2 [simp]: "b \<noteq> (0::int) ==> (b*a) div b = a"
wenzelm@23164
   795
by (subst mult_commute, erule zdiv_zmult_self1)
wenzelm@23164
   796
wenzelm@23164
   797
lemma zmod_zmult_self1 [simp]: "(a*b) mod b = (0::int)"
wenzelm@23164
   798
by (simp add: zmod_zmult1_eq)
wenzelm@23164
   799
wenzelm@23164
   800
lemma zmod_zmult_self2 [simp]: "(b*a) mod b = (0::int)"
wenzelm@23164
   801
by (simp add: mult_commute zmod_zmult1_eq)
wenzelm@23164
   802
wenzelm@23164
   803
lemma zmod_eq_0_iff: "(m mod d = 0) = (EX q::int. m = d*q)"
wenzelm@23164
   804
proof
wenzelm@23164
   805
  assume "m mod d = 0"
wenzelm@23164
   806
  with zmod_zdiv_equality[of m d] show "EX q::int. m = d*q" by auto
wenzelm@23164
   807
next
wenzelm@23164
   808
  assume "EX q::int. m = d*q"
wenzelm@23164
   809
  thus "m mod d = 0" by auto
wenzelm@23164
   810
qed
wenzelm@23164
   811
wenzelm@23164
   812
lemmas zmod_eq_0D [dest!] = zmod_eq_0_iff [THEN iffD1]
wenzelm@23164
   813
wenzelm@23164
   814
lemma zmod_zadd_left_eq: "(a+b) mod (c::int) = ((a mod c) + b) mod c"
wenzelm@23164
   815
apply (rule trans [symmetric])
wenzelm@23164
   816
apply (rule zmod_zadd1_eq, simp)
wenzelm@23164
   817
apply (rule zmod_zadd1_eq [symmetric])
wenzelm@23164
   818
done
wenzelm@23164
   819
wenzelm@23164
   820
lemma zmod_zadd_right_eq: "(a+b) mod (c::int) = (a + (b mod c)) mod c"
wenzelm@23164
   821
apply (rule trans [symmetric])
wenzelm@23164
   822
apply (rule zmod_zadd1_eq, simp)
wenzelm@23164
   823
apply (rule zmod_zadd1_eq [symmetric])
wenzelm@23164
   824
done
wenzelm@23164
   825
wenzelm@23164
   826
lemma zmod_zadd_self1[simp]: "(a+b) mod a = b mod (a::int)"
wenzelm@23164
   827
apply (case_tac "a = 0", simp)
wenzelm@23164
   828
apply (simp add: zmod_zadd1_eq)
wenzelm@23164
   829
done
wenzelm@23164
   830
wenzelm@23164
   831
lemma zmod_zadd_self2[simp]: "(b+a) mod a = b mod (a::int)"
wenzelm@23164
   832
apply (case_tac "a = 0", simp)
wenzelm@23164
   833
apply (simp add: zmod_zadd1_eq)
wenzelm@23164
   834
done
wenzelm@23164
   835
wenzelm@23164
   836
nipkow@23983
   837
lemma zmod_zdiff1_eq: fixes a::int
nipkow@23983
   838
  shows "(a - b) mod c = (a mod c - b mod c) mod c" (is "?l = ?r")
nipkow@23983
   839
proof -
nipkow@23983
   840
  have "?l = (c + (a mod c - b mod c)) mod c"
nipkow@23983
   841
    using zmod_zadd1_eq[of a "-b" c] by(simp add:ring_simps zmod_zminus1_eq_if)
nipkow@23983
   842
  also have "\<dots> = ?r" by simp
nipkow@23983
   843
  finally show ?thesis .
nipkow@23983
   844
qed
nipkow@23983
   845
wenzelm@23164
   846
subsection{*Proving  @{term "a div (b*c) = (a div b) div c"} *}
wenzelm@23164
   847
wenzelm@23164
   848
(*The condition c>0 seems necessary.  Consider that 7 div ~6 = ~2 but
wenzelm@23164
   849
  7 div 2 div ~3 = 3 div ~3 = ~1.  The subcase (a div b) mod c = 0 seems
wenzelm@23164
   850
  to cause particular problems.*)
wenzelm@23164
   851
wenzelm@23164
   852
text{*first, four lemmas to bound the remainder for the cases b<0 and b>0 *}
wenzelm@23164
   853
wenzelm@23164
   854
lemma zmult2_lemma_aux1: "[| (0::int) < c;  b < r;  r \<le> 0 |] ==> b*c < b*(q mod c) + r"
wenzelm@23164
   855
apply (subgoal_tac "b * (c - q mod c) < r * 1")
wenzelm@23164
   856
apply (simp add: right_diff_distrib)
wenzelm@23164
   857
apply (rule order_le_less_trans)
wenzelm@23164
   858
apply (erule_tac [2] mult_strict_right_mono)
wenzelm@23164
   859
apply (rule mult_left_mono_neg)
wenzelm@23164
   860
apply (auto simp add: compare_rls add_commute [of 1]
wenzelm@23164
   861
                      add1_zle_eq pos_mod_bound)
wenzelm@23164
   862
done
wenzelm@23164
   863
wenzelm@23164
   864
lemma zmult2_lemma_aux2:
wenzelm@23164
   865
     "[| (0::int) < c;   b < r;  r \<le> 0 |] ==> b * (q mod c) + r \<le> 0"
wenzelm@23164
   866
apply (subgoal_tac "b * (q mod c) \<le> 0")
wenzelm@23164
   867
 apply arith
wenzelm@23164
   868
apply (simp add: mult_le_0_iff)
wenzelm@23164
   869
done
wenzelm@23164
   870
wenzelm@23164
   871
lemma zmult2_lemma_aux3: "[| (0::int) < c;  0 \<le> r;  r < b |] ==> 0 \<le> b * (q mod c) + r"
wenzelm@23164
   872
apply (subgoal_tac "0 \<le> b * (q mod c) ")
wenzelm@23164
   873
apply arith
wenzelm@23164
   874
apply (simp add: zero_le_mult_iff)
wenzelm@23164
   875
done
wenzelm@23164
   876
wenzelm@23164
   877
lemma zmult2_lemma_aux4: "[| (0::int) < c; 0 \<le> r; r < b |] ==> b * (q mod c) + r < b * c"
wenzelm@23164
   878
apply (subgoal_tac "r * 1 < b * (c - q mod c) ")
wenzelm@23164
   879
apply (simp add: right_diff_distrib)
wenzelm@23164
   880
apply (rule order_less_le_trans)
wenzelm@23164
   881
apply (erule mult_strict_right_mono)
wenzelm@23164
   882
apply (rule_tac [2] mult_left_mono)
wenzelm@23164
   883
apply (auto simp add: compare_rls add_commute [of 1]
wenzelm@23164
   884
                      add1_zle_eq pos_mod_bound)
wenzelm@23164
   885
done
wenzelm@23164
   886
wenzelm@23164
   887
lemma zmult2_lemma: "[| quorem ((a,b), (q,r));  b \<noteq> 0;  0 < c |]  
wenzelm@23164
   888
      ==> quorem ((a, b*c), (q div c, b*(q mod c) + r))"
wenzelm@23164
   889
by (auto simp add: mult_ac quorem_def linorder_neq_iff
wenzelm@23164
   890
                   zero_less_mult_iff right_distrib [symmetric] 
wenzelm@23164
   891
                   zmult2_lemma_aux1 zmult2_lemma_aux2 zmult2_lemma_aux3 zmult2_lemma_aux4)
wenzelm@23164
   892
wenzelm@23164
   893
lemma zdiv_zmult2_eq: "(0::int) < c ==> a div (b*c) = (a div b) div c"
wenzelm@23164
   894
apply (case_tac "b = 0", simp)
wenzelm@23164
   895
apply (force simp add: quorem_div_mod [THEN zmult2_lemma, THEN quorem_div])
wenzelm@23164
   896
done
wenzelm@23164
   897
wenzelm@23164
   898
lemma zmod_zmult2_eq:
wenzelm@23164
   899
     "(0::int) < c ==> a mod (b*c) = b*(a div b mod c) + a mod b"
wenzelm@23164
   900
apply (case_tac "b = 0", simp)
wenzelm@23164
   901
apply (force simp add: quorem_div_mod [THEN zmult2_lemma, THEN quorem_mod])
wenzelm@23164
   902
done
wenzelm@23164
   903
wenzelm@23164
   904
wenzelm@23164
   905
subsection{*Cancellation of Common Factors in div*}
wenzelm@23164
   906
wenzelm@23164
   907
lemma zdiv_zmult_zmult1_aux1:
wenzelm@23164
   908
     "[| (0::int) < b;  c \<noteq> 0 |] ==> (c*a) div (c*b) = a div b"
wenzelm@23164
   909
by (subst zdiv_zmult2_eq, auto)
wenzelm@23164
   910
wenzelm@23164
   911
lemma zdiv_zmult_zmult1_aux2:
wenzelm@23164
   912
     "[| b < (0::int);  c \<noteq> 0 |] ==> (c*a) div (c*b) = a div b"
wenzelm@23164
   913
apply (subgoal_tac " (c * (-a)) div (c * (-b)) = (-a) div (-b) ")
wenzelm@23164
   914
apply (rule_tac [2] zdiv_zmult_zmult1_aux1, auto)
wenzelm@23164
   915
done
wenzelm@23164
   916
wenzelm@23164
   917
lemma zdiv_zmult_zmult1: "c \<noteq> (0::int) ==> (c*a) div (c*b) = a div b"
wenzelm@23164
   918
apply (case_tac "b = 0", simp)
wenzelm@23164
   919
apply (auto simp add: linorder_neq_iff zdiv_zmult_zmult1_aux1 zdiv_zmult_zmult1_aux2)
wenzelm@23164
   920
done
wenzelm@23164
   921
nipkow@23401
   922
lemma zdiv_zmult_zmult1_if[simp]:
nipkow@23401
   923
  "(k*m) div (k*n) = (if k = (0::int) then 0 else m div n)"
nipkow@23401
   924
by (simp add:zdiv_zmult_zmult1)
nipkow@23401
   925
nipkow@23401
   926
(*
wenzelm@23164
   927
lemma zdiv_zmult_zmult2: "c \<noteq> (0::int) ==> (a*c) div (b*c) = a div b"
wenzelm@23164
   928
apply (drule zdiv_zmult_zmult1)
wenzelm@23164
   929
apply (auto simp add: mult_commute)
wenzelm@23164
   930
done
nipkow@23401
   931
*)
wenzelm@23164
   932
wenzelm@23164
   933
wenzelm@23164
   934
subsection{*Distribution of Factors over mod*}
wenzelm@23164
   935
wenzelm@23164
   936
lemma zmod_zmult_zmult1_aux1:
wenzelm@23164
   937
     "[| (0::int) < b;  c \<noteq> 0 |] ==> (c*a) mod (c*b) = c * (a mod b)"
wenzelm@23164
   938
by (subst zmod_zmult2_eq, auto)
wenzelm@23164
   939
wenzelm@23164
   940
lemma zmod_zmult_zmult1_aux2:
wenzelm@23164
   941
     "[| b < (0::int);  c \<noteq> 0 |] ==> (c*a) mod (c*b) = c * (a mod b)"
wenzelm@23164
   942
apply (subgoal_tac " (c * (-a)) mod (c * (-b)) = c * ((-a) mod (-b))")
wenzelm@23164
   943
apply (rule_tac [2] zmod_zmult_zmult1_aux1, auto)
wenzelm@23164
   944
done
wenzelm@23164
   945
wenzelm@23164
   946
lemma zmod_zmult_zmult1: "(c*a) mod (c*b) = (c::int) * (a mod b)"
wenzelm@23164
   947
apply (case_tac "b = 0", simp)
wenzelm@23164
   948
apply (case_tac "c = 0", simp)
wenzelm@23164
   949
apply (auto simp add: linorder_neq_iff zmod_zmult_zmult1_aux1 zmod_zmult_zmult1_aux2)
wenzelm@23164
   950
done
wenzelm@23164
   951
wenzelm@23164
   952
lemma zmod_zmult_zmult2: "(a*c) mod (b*c) = (a mod b) * (c::int)"
wenzelm@23164
   953
apply (cut_tac c = c in zmod_zmult_zmult1)
wenzelm@23164
   954
apply (auto simp add: mult_commute)
wenzelm@23164
   955
done
wenzelm@23164
   956
nipkow@24490
   957
lemma zmod_zmod_cancel:
nipkow@24490
   958
assumes "n dvd m" shows "(k::int) mod m mod n = k mod n"
nipkow@24490
   959
proof -
nipkow@24490
   960
  from `n dvd m` obtain r where "m = n*r" by(auto simp:dvd_def)
nipkow@24490
   961
  have "k mod n = (m * (k div m) + k mod m) mod n"
nipkow@24490
   962
    using zmod_zdiv_equality[of k m] by simp
nipkow@24490
   963
  also have "\<dots> = (m * (k div m) mod n + k mod m mod n) mod n"
nipkow@24490
   964
    by(subst zmod_zadd1_eq, rule refl)
nipkow@24490
   965
  also have "m * (k div m) mod n = 0" using `m = n*r`
nipkow@24490
   966
    by(simp add:mult_ac)
nipkow@24490
   967
  finally show ?thesis by simp
nipkow@24490
   968
qed
nipkow@24490
   969
wenzelm@23164
   970
wenzelm@23164
   971
subsection {*Splitting Rules for div and mod*}
wenzelm@23164
   972
wenzelm@23164
   973
text{*The proofs of the two lemmas below are essentially identical*}
wenzelm@23164
   974
wenzelm@23164
   975
lemma split_pos_lemma:
wenzelm@23164
   976
 "0<k ==> 
wenzelm@23164
   977
    P(n div k :: int)(n mod k) = (\<forall>i j. 0\<le>j & j<k & n = k*i + j --> P i j)"
wenzelm@23164
   978
apply (rule iffI, clarify)
wenzelm@23164
   979
 apply (erule_tac P="P ?x ?y" in rev_mp)  
wenzelm@23164
   980
 apply (subst zmod_zadd1_eq) 
wenzelm@23164
   981
 apply (subst zdiv_zadd1_eq) 
wenzelm@23164
   982
 apply (simp add: div_pos_pos_trivial mod_pos_pos_trivial)  
wenzelm@23164
   983
txt{*converse direction*}
wenzelm@23164
   984
apply (drule_tac x = "n div k" in spec) 
wenzelm@23164
   985
apply (drule_tac x = "n mod k" in spec, simp)
wenzelm@23164
   986
done
wenzelm@23164
   987
wenzelm@23164
   988
lemma split_neg_lemma:
wenzelm@23164
   989
 "k<0 ==>
wenzelm@23164
   990
    P(n div k :: int)(n mod k) = (\<forall>i j. k<j & j\<le>0 & n = k*i + j --> P i j)"
wenzelm@23164
   991
apply (rule iffI, clarify)
wenzelm@23164
   992
 apply (erule_tac P="P ?x ?y" in rev_mp)  
wenzelm@23164
   993
 apply (subst zmod_zadd1_eq) 
wenzelm@23164
   994
 apply (subst zdiv_zadd1_eq) 
wenzelm@23164
   995
 apply (simp add: div_neg_neg_trivial mod_neg_neg_trivial)  
wenzelm@23164
   996
txt{*converse direction*}
wenzelm@23164
   997
apply (drule_tac x = "n div k" in spec) 
wenzelm@23164
   998
apply (drule_tac x = "n mod k" in spec, simp)
wenzelm@23164
   999
done
wenzelm@23164
  1000
wenzelm@23164
  1001
lemma split_zdiv:
wenzelm@23164
  1002
 "P(n div k :: int) =
wenzelm@23164
  1003
  ((k = 0 --> P 0) & 
wenzelm@23164
  1004
   (0<k --> (\<forall>i j. 0\<le>j & j<k & n = k*i + j --> P i)) & 
wenzelm@23164
  1005
   (k<0 --> (\<forall>i j. k<j & j\<le>0 & n = k*i + j --> P i)))"
wenzelm@23164
  1006
apply (case_tac "k=0", simp)
wenzelm@23164
  1007
apply (simp only: linorder_neq_iff)
wenzelm@23164
  1008
apply (erule disjE) 
wenzelm@23164
  1009
 apply (simp_all add: split_pos_lemma [of concl: "%x y. P x"] 
wenzelm@23164
  1010
                      split_neg_lemma [of concl: "%x y. P x"])
wenzelm@23164
  1011
done
wenzelm@23164
  1012
wenzelm@23164
  1013
lemma split_zmod:
wenzelm@23164
  1014
 "P(n mod k :: int) =
wenzelm@23164
  1015
  ((k = 0 --> P n) & 
wenzelm@23164
  1016
   (0<k --> (\<forall>i j. 0\<le>j & j<k & n = k*i + j --> P j)) & 
wenzelm@23164
  1017
   (k<0 --> (\<forall>i j. k<j & j\<le>0 & n = k*i + j --> P j)))"
wenzelm@23164
  1018
apply (case_tac "k=0", simp)
wenzelm@23164
  1019
apply (simp only: linorder_neq_iff)
wenzelm@23164
  1020
apply (erule disjE) 
wenzelm@23164
  1021
 apply (simp_all add: split_pos_lemma [of concl: "%x y. P y"] 
wenzelm@23164
  1022
                      split_neg_lemma [of concl: "%x y. P y"])
wenzelm@23164
  1023
done
wenzelm@23164
  1024
wenzelm@23164
  1025
(* Enable arith to deal with div 2 and mod 2: *)
wenzelm@23164
  1026
declare split_zdiv [of _ _ "number_of k", simplified, standard, arith_split]
wenzelm@23164
  1027
declare split_zmod [of _ _ "number_of k", simplified, standard, arith_split]
wenzelm@23164
  1028
wenzelm@23164
  1029
wenzelm@23164
  1030
subsection{*Speeding up the Division Algorithm with Shifting*}
wenzelm@23164
  1031
wenzelm@23164
  1032
text{*computing div by shifting *}
wenzelm@23164
  1033
wenzelm@23164
  1034
lemma pos_zdiv_mult_2: "(0::int) \<le> a ==> (1 + 2*b) div (2*a) = b div a"
wenzelm@23164
  1035
proof cases
wenzelm@23164
  1036
  assume "a=0"
wenzelm@23164
  1037
    thus ?thesis by simp
wenzelm@23164
  1038
next
wenzelm@23164
  1039
  assume "a\<noteq>0" and le_a: "0\<le>a"   
wenzelm@23164
  1040
  hence a_pos: "1 \<le> a" by arith
wenzelm@23164
  1041
  hence one_less_a2: "1 < 2*a" by arith
wenzelm@23164
  1042
  hence le_2a: "2 * (1 + b mod a) \<le> 2 * a"
wenzelm@23164
  1043
    by (simp add: mult_le_cancel_left add_commute [of 1] add1_zle_eq)
wenzelm@23164
  1044
  with a_pos have "0 \<le> b mod a" by simp
wenzelm@23164
  1045
  hence le_addm: "0 \<le> 1 mod (2*a) + 2*(b mod a)"
wenzelm@23164
  1046
    by (simp add: mod_pos_pos_trivial one_less_a2)
wenzelm@23164
  1047
  with  le_2a
wenzelm@23164
  1048
  have "(1 mod (2*a) + 2*(b mod a)) div (2*a) = 0"
wenzelm@23164
  1049
    by (simp add: div_pos_pos_trivial le_addm mod_pos_pos_trivial one_less_a2
wenzelm@23164
  1050
                  right_distrib) 
wenzelm@23164
  1051
  thus ?thesis
wenzelm@23164
  1052
    by (subst zdiv_zadd1_eq,
wenzelm@23164
  1053
        simp add: zdiv_zmult_zmult1 zmod_zmult_zmult1 one_less_a2
wenzelm@23164
  1054
                  div_pos_pos_trivial)
wenzelm@23164
  1055
qed
wenzelm@23164
  1056
wenzelm@23164
  1057
lemma neg_zdiv_mult_2: "a \<le> (0::int) ==> (1 + 2*b) div (2*a) = (b+1) div a"
wenzelm@23164
  1058
apply (subgoal_tac " (1 + 2* (-b - 1)) div (2 * (-a)) = (-b - 1) div (-a) ")
wenzelm@23164
  1059
apply (rule_tac [2] pos_zdiv_mult_2)
wenzelm@23164
  1060
apply (auto simp add: minus_mult_right [symmetric] right_diff_distrib)
wenzelm@23164
  1061
apply (subgoal_tac " (-1 - (2 * b)) = - (1 + (2 * b))")
wenzelm@23164
  1062
apply (simp only: zdiv_zminus_zminus diff_minus minus_add_distrib [symmetric],
wenzelm@23164
  1063
       simp) 
wenzelm@23164
  1064
done
wenzelm@23164
  1065
wenzelm@23164
  1066
(*Not clear why this must be proved separately; probably number_of causes
wenzelm@23164
  1067
  simplification problems*)
wenzelm@23164
  1068
lemma not_0_le_lemma: "~ 0 \<le> x ==> x \<le> (0::int)"
wenzelm@23164
  1069
by auto
wenzelm@23164
  1070
huffman@26086
  1071
lemma zdiv_number_of_Bit0 [simp]:
huffman@26086
  1072
     "number_of (Int.Bit0 v) div number_of (Int.Bit0 w) =  
huffman@26086
  1073
          number_of v div (number_of w :: int)"
huffman@26086
  1074
by (simp only: number_of_eq numeral_simps) simp
huffman@26086
  1075
huffman@26086
  1076
lemma zdiv_number_of_Bit1 [simp]:
huffman@26086
  1077
     "number_of (Int.Bit1 v) div number_of (Int.Bit0 w) =  
huffman@26086
  1078
          (if (0::int) \<le> number_of w                    
wenzelm@23164
  1079
           then number_of v div (number_of w)     
wenzelm@23164
  1080
           else (number_of v + (1::int)) div (number_of w))"
wenzelm@23164
  1081
apply (simp only: number_of_eq numeral_simps UNIV_I split: split_if) 
huffman@26086
  1082
apply (simp add: zdiv_zmult_zmult1 pos_zdiv_mult_2 neg_zdiv_mult_2 add_ac)
wenzelm@23164
  1083
done
wenzelm@23164
  1084
wenzelm@23164
  1085
wenzelm@23164
  1086
subsection{*Computing mod by Shifting (proofs resemble those for div)*}
wenzelm@23164
  1087
wenzelm@23164
  1088
lemma pos_zmod_mult_2:
wenzelm@23164
  1089
     "(0::int) \<le> a ==> (1 + 2*b) mod (2*a) = 1 + 2 * (b mod a)"
wenzelm@23164
  1090
apply (case_tac "a = 0", simp)
wenzelm@23164
  1091
apply (subgoal_tac "1 < a * 2")
wenzelm@23164
  1092
 prefer 2 apply arith
wenzelm@23164
  1093
apply (subgoal_tac "2* (1 + b mod a) \<le> 2*a")
wenzelm@23164
  1094
 apply (rule_tac [2] mult_left_mono)
wenzelm@23164
  1095
apply (auto simp add: add_commute [of 1] mult_commute add1_zle_eq 
wenzelm@23164
  1096
                      pos_mod_bound)
wenzelm@23164
  1097
apply (subst zmod_zadd1_eq)
wenzelm@23164
  1098
apply (simp add: zmod_zmult_zmult2 mod_pos_pos_trivial)
wenzelm@23164
  1099
apply (rule mod_pos_pos_trivial)
huffman@26086
  1100
apply (auto simp add: mod_pos_pos_trivial ring_distribs)
wenzelm@23164
  1101
apply (subgoal_tac "0 \<le> b mod a", arith, simp)
wenzelm@23164
  1102
done
wenzelm@23164
  1103
wenzelm@23164
  1104
lemma neg_zmod_mult_2:
wenzelm@23164
  1105
     "a \<le> (0::int) ==> (1 + 2*b) mod (2*a) = 2 * ((b+1) mod a) - 1"
wenzelm@23164
  1106
apply (subgoal_tac "(1 + 2* (-b - 1)) mod (2* (-a)) = 
wenzelm@23164
  1107
                    1 + 2* ((-b - 1) mod (-a))")
wenzelm@23164
  1108
apply (rule_tac [2] pos_zmod_mult_2)
wenzelm@23164
  1109
apply (auto simp add: minus_mult_right [symmetric] right_diff_distrib)
wenzelm@23164
  1110
apply (subgoal_tac " (-1 - (2 * b)) = - (1 + (2 * b))")
wenzelm@23164
  1111
 prefer 2 apply simp 
wenzelm@23164
  1112
apply (simp only: zmod_zminus_zminus diff_minus minus_add_distrib [symmetric])
wenzelm@23164
  1113
done
wenzelm@23164
  1114
huffman@26086
  1115
lemma zmod_number_of_Bit0 [simp]:
huffman@26086
  1116
     "number_of (Int.Bit0 v) mod number_of (Int.Bit0 w) =  
huffman@26086
  1117
      (2::int) * (number_of v mod number_of w)"
huffman@26086
  1118
apply (simp only: number_of_eq numeral_simps) 
huffman@26086
  1119
apply (simp add: zmod_zmult_zmult1 pos_zmod_mult_2 
huffman@26086
  1120
                 not_0_le_lemma neg_zmod_mult_2 add_ac)
huffman@26086
  1121
done
huffman@26086
  1122
huffman@26086
  1123
lemma zmod_number_of_Bit1 [simp]:
huffman@26086
  1124
     "number_of (Int.Bit1 v) mod number_of (Int.Bit0 w) =  
huffman@26086
  1125
      (if (0::int) \<le> number_of w  
wenzelm@23164
  1126
                then 2 * (number_of v mod number_of w) + 1     
wenzelm@23164
  1127
                else 2 * ((number_of v + (1::int)) mod number_of w) - 1)"
huffman@26086
  1128
apply (simp only: number_of_eq numeral_simps) 
wenzelm@23164
  1129
apply (simp add: zmod_zmult_zmult1 pos_zmod_mult_2 
wenzelm@23164
  1130
                 not_0_le_lemma neg_zmod_mult_2 add_ac)
wenzelm@23164
  1131
done
wenzelm@23164
  1132
wenzelm@23164
  1133
wenzelm@23164
  1134
subsection{*Quotients of Signs*}
wenzelm@23164
  1135
wenzelm@23164
  1136
lemma div_neg_pos_less0: "[| a < (0::int);  0 < b |] ==> a div b < 0"
wenzelm@23164
  1137
apply (subgoal_tac "a div b \<le> -1", force)
wenzelm@23164
  1138
apply (rule order_trans)
wenzelm@23164
  1139
apply (rule_tac a' = "-1" in zdiv_mono1)
wenzelm@23164
  1140
apply (auto simp add: zdiv_minus1)
wenzelm@23164
  1141
done
wenzelm@23164
  1142
wenzelm@23164
  1143
lemma div_nonneg_neg_le0: "[| (0::int) \<le> a;  b < 0 |] ==> a div b \<le> 0"
wenzelm@23164
  1144
by (drule zdiv_mono1_neg, auto)
wenzelm@23164
  1145
wenzelm@23164
  1146
lemma pos_imp_zdiv_nonneg_iff: "(0::int) < b ==> (0 \<le> a div b) = (0 \<le> a)"
wenzelm@23164
  1147
apply auto
wenzelm@23164
  1148
apply (drule_tac [2] zdiv_mono1)
wenzelm@23164
  1149
apply (auto simp add: linorder_neq_iff)
wenzelm@23164
  1150
apply (simp (no_asm_use) add: linorder_not_less [symmetric])
wenzelm@23164
  1151
apply (blast intro: div_neg_pos_less0)
wenzelm@23164
  1152
done
wenzelm@23164
  1153
wenzelm@23164
  1154
lemma neg_imp_zdiv_nonneg_iff:
wenzelm@23164
  1155
     "b < (0::int) ==> (0 \<le> a div b) = (a \<le> (0::int))"
wenzelm@23164
  1156
apply (subst zdiv_zminus_zminus [symmetric])
wenzelm@23164
  1157
apply (subst pos_imp_zdiv_nonneg_iff, auto)
wenzelm@23164
  1158
done
wenzelm@23164
  1159
wenzelm@23164
  1160
(*But not (a div b \<le> 0 iff a\<le>0); consider a=1, b=2 when a div b = 0.*)
wenzelm@23164
  1161
lemma pos_imp_zdiv_neg_iff: "(0::int) < b ==> (a div b < 0) = (a < 0)"
wenzelm@23164
  1162
by (simp add: linorder_not_le [symmetric] pos_imp_zdiv_nonneg_iff)
wenzelm@23164
  1163
wenzelm@23164
  1164
(*Again the law fails for \<le>: consider a = -1, b = -2 when a div b = 0*)
wenzelm@23164
  1165
lemma neg_imp_zdiv_neg_iff: "b < (0::int) ==> (a div b < 0) = (0 < a)"
wenzelm@23164
  1166
by (simp add: linorder_not_le [symmetric] neg_imp_zdiv_nonneg_iff)
wenzelm@23164
  1167
wenzelm@23164
  1168
wenzelm@23164
  1169
subsection {* The Divides Relation *}
wenzelm@23164
  1170
wenzelm@23164
  1171
lemma zdvd_iff_zmod_eq_0: "(m dvd n) = (n mod m = (0::int))"
haftmann@23512
  1172
  by (simp add: dvd_def zmod_eq_0_iff)
haftmann@23512
  1173
wenzelm@23164
  1174
lemmas zdvd_iff_zmod_eq_0_number_of [simp] =
wenzelm@23164
  1175
  zdvd_iff_zmod_eq_0 [of "number_of x" "number_of y", standard]
wenzelm@23164
  1176
wenzelm@23164
  1177
lemma zdvd_0_right [iff]: "(m::int) dvd 0"
haftmann@23512
  1178
  by (simp add: dvd_def)
wenzelm@23164
  1179
paulson@24286
  1180
lemma zdvd_0_left [iff,noatp]: "(0 dvd (m::int)) = (m = 0)"
wenzelm@23164
  1181
  by (simp add: dvd_def)
wenzelm@23164
  1182
wenzelm@23164
  1183
lemma zdvd_1_left [iff]: "1 dvd (m::int)"
wenzelm@23164
  1184
  by (simp add: dvd_def)
wenzelm@23164
  1185
wenzelm@23164
  1186
lemma zdvd_refl [simp]: "m dvd (m::int)"
haftmann@23512
  1187
  by (auto simp add: dvd_def intro: zmult_1_right [symmetric])
wenzelm@23164
  1188
wenzelm@23164
  1189
lemma zdvd_trans: "m dvd n ==> n dvd k ==> m dvd (k::int)"
haftmann@23512
  1190
  by (auto simp add: dvd_def intro: mult_assoc)
wenzelm@23164
  1191
haftmann@27651
  1192
lemma zdvd_zminus_iff: "m dvd -n \<longleftrightarrow> m dvd (n::int)"
haftmann@27651
  1193
proof
haftmann@27651
  1194
  assume "m dvd - n"
haftmann@27651
  1195
  then obtain k where "- n = m * k" ..
haftmann@27651
  1196
  then have "n = m * - k" by simp
haftmann@27651
  1197
  then show "m dvd n" ..
haftmann@27651
  1198
next
haftmann@27651
  1199
  assume "m dvd n"
haftmann@27651
  1200
  then have "m dvd n * -1" by (rule dvd_mult2)
haftmann@27651
  1201
  then show "m dvd - n" by simp
haftmann@27651
  1202
qed
wenzelm@23164
  1203
haftmann@27651
  1204
lemma zdvd_zminus2_iff: "-m dvd n \<longleftrightarrow> m dvd (n::int)"
haftmann@27651
  1205
proof
haftmann@27651
  1206
  assume "- m dvd n"
haftmann@27651
  1207
  then obtain k where "n = - m * k" ..
haftmann@27651
  1208
  then have "n = m * - k" by simp
haftmann@27651
  1209
  then show "m dvd n" ..
haftmann@27651
  1210
next
haftmann@27651
  1211
  assume "m dvd n"
haftmann@27651
  1212
  then obtain k where "n = m * k" ..
haftmann@27651
  1213
  then have "n = - m * - k" by simp
haftmann@27651
  1214
  then show "- m dvd n" ..
haftmann@27651
  1215
qed
haftmann@27651
  1216
wenzelm@23164
  1217
lemma zdvd_abs1: "( \<bar>i::int\<bar> dvd j) = (i dvd j)" 
haftmann@27651
  1218
  by (cases "i > 0") (simp_all add: zdvd_zminus2_iff)
haftmann@27651
  1219
wenzelm@23164
  1220
lemma zdvd_abs2: "( (i::int) dvd \<bar>j\<bar>) = (i dvd j)" 
haftmann@27651
  1221
  by (cases "j > 0") (simp_all add: zdvd_zminus_iff)
wenzelm@23164
  1222
wenzelm@23164
  1223
lemma zdvd_anti_sym:
wenzelm@23164
  1224
    "0 < m ==> 0 < n ==> m dvd n ==> n dvd m ==> m = (n::int)"
wenzelm@23164
  1225
  apply (simp add: dvd_def, auto)
wenzelm@23164
  1226
  apply (simp add: mult_assoc zero_less_mult_iff zmult_eq_1_iff)
wenzelm@23164
  1227
  done
wenzelm@23164
  1228
wenzelm@23164
  1229
lemma zdvd_zadd: "k dvd m ==> k dvd n ==> k dvd (m + n :: int)"
wenzelm@23164
  1230
  apply (simp add: dvd_def)
wenzelm@23164
  1231
  apply (blast intro: right_distrib [symmetric])
wenzelm@23164
  1232
  done
wenzelm@23164
  1233
wenzelm@23164
  1234
lemma zdvd_dvd_eq: assumes anz:"a \<noteq> 0" and ab: "(a::int) dvd b" and ba:"b dvd a" 
wenzelm@23164
  1235
  shows "\<bar>a\<bar> = \<bar>b\<bar>"
wenzelm@23164
  1236
proof-
wenzelm@23164
  1237
  from ab obtain k where k:"b = a*k" unfolding dvd_def by blast 
wenzelm@23164
  1238
  from ba obtain k' where k':"a = b*k'" unfolding dvd_def by blast 
wenzelm@23164
  1239
  from k k' have "a = a*k*k'" by simp
wenzelm@23164
  1240
  with mult_cancel_left1[where c="a" and b="k*k'"]
wenzelm@23164
  1241
  have kk':"k*k' = 1" using anz by (simp add: mult_assoc)
wenzelm@23164
  1242
  hence "k = 1 \<and> k' = 1 \<or> k = -1 \<and> k' = -1" by (simp add: zmult_eq_1_iff)
wenzelm@23164
  1243
  thus ?thesis using k k' by auto
wenzelm@23164
  1244
qed
wenzelm@23164
  1245
wenzelm@23164
  1246
lemma zdvd_zdiff: "k dvd m ==> k dvd n ==> k dvd (m - n :: int)"
wenzelm@23164
  1247
  apply (simp add: dvd_def)
wenzelm@23164
  1248
  apply (blast intro: right_diff_distrib [symmetric])
wenzelm@23164
  1249
  done
wenzelm@23164
  1250
wenzelm@23164
  1251
lemma zdvd_zdiffD: "k dvd m - n ==> k dvd n ==> k dvd (m::int)"
wenzelm@23164
  1252
  apply (subgoal_tac "m = n + (m - n)")
wenzelm@23164
  1253
   apply (erule ssubst)
wenzelm@23164
  1254
   apply (blast intro: zdvd_zadd, simp)
wenzelm@23164
  1255
  done
wenzelm@23164
  1256
wenzelm@23164
  1257
lemma zdvd_zmult: "k dvd (n::int) ==> k dvd m * n"
wenzelm@23164
  1258
  apply (simp add: dvd_def)
wenzelm@23164
  1259
  apply (blast intro: mult_left_commute)
wenzelm@23164
  1260
  done
wenzelm@23164
  1261
wenzelm@23164
  1262
lemma zdvd_zmult2: "k dvd (m::int) ==> k dvd m * n"
wenzelm@23164
  1263
  apply (subst mult_commute)
wenzelm@23164
  1264
  apply (erule zdvd_zmult)
wenzelm@23164
  1265
  done
wenzelm@23164
  1266
wenzelm@23164
  1267
lemma zdvd_triv_right [iff]: "(k::int) dvd m * k"
wenzelm@23164
  1268
  apply (rule zdvd_zmult)
wenzelm@23164
  1269
  apply (rule zdvd_refl)
wenzelm@23164
  1270
  done
wenzelm@23164
  1271
wenzelm@23164
  1272
lemma zdvd_triv_left [iff]: "(k::int) dvd k * m"
wenzelm@23164
  1273
  apply (rule zdvd_zmult2)
wenzelm@23164
  1274
  apply (rule zdvd_refl)
wenzelm@23164
  1275
  done
wenzelm@23164
  1276
wenzelm@23164
  1277
lemma zdvd_zmultD2: "j * k dvd n ==> j dvd (n::int)"
wenzelm@23164
  1278
  apply (simp add: dvd_def)
wenzelm@23164
  1279
  apply (simp add: mult_assoc, blast)
wenzelm@23164
  1280
  done
wenzelm@23164
  1281
wenzelm@23164
  1282
lemma zdvd_zmultD: "j * k dvd n ==> k dvd (n::int)"
wenzelm@23164
  1283
  apply (rule zdvd_zmultD2)
wenzelm@23164
  1284
  apply (subst mult_commute, assumption)
wenzelm@23164
  1285
  done
wenzelm@23164
  1286
wenzelm@23164
  1287
lemma zdvd_zmult_mono: "i dvd m ==> j dvd (n::int) ==> i * j dvd m * n"
haftmann@27651
  1288
  by (rule mult_dvd_mono)
wenzelm@23164
  1289
wenzelm@23164
  1290
lemma zdvd_reduce: "(k dvd n + k * m) = (k dvd (n::int))"
wenzelm@23164
  1291
  apply (rule iffI)
wenzelm@23164
  1292
   apply (erule_tac [2] zdvd_zadd)
wenzelm@23164
  1293
   apply (subgoal_tac "n = (n + k * m) - k * m")
wenzelm@23164
  1294
    apply (erule ssubst)
wenzelm@23164
  1295
    apply (erule zdvd_zdiff, simp_all)
wenzelm@23164
  1296
  done
wenzelm@23164
  1297
wenzelm@23164
  1298
lemma zdvd_zmod: "f dvd m ==> f dvd (n::int) ==> f dvd m mod n"
wenzelm@23164
  1299
  apply (simp add: dvd_def)
wenzelm@23164
  1300
  apply (auto simp add: zmod_zmult_zmult1)
wenzelm@23164
  1301
  done
wenzelm@23164
  1302
wenzelm@23164
  1303
lemma zdvd_zmod_imp_zdvd: "k dvd m mod n ==> k dvd n ==> k dvd (m::int)"
wenzelm@23164
  1304
  apply (subgoal_tac "k dvd n * (m div n) + m mod n")
wenzelm@23164
  1305
   apply (simp add: zmod_zdiv_equality [symmetric])
wenzelm@23164
  1306
  apply (simp only: zdvd_zadd zdvd_zmult2)
wenzelm@23164
  1307
  done
wenzelm@23164
  1308
wenzelm@23164
  1309
lemma zdvd_not_zless: "0 < m ==> m < n ==> \<not> n dvd (m::int)"
haftmann@27651
  1310
  apply (auto elim!: dvdE)
wenzelm@23164
  1311
  apply (subgoal_tac "0 < n")
wenzelm@23164
  1312
   prefer 2
wenzelm@23164
  1313
   apply (blast intro: order_less_trans)
wenzelm@23164
  1314
  apply (simp add: zero_less_mult_iff)
wenzelm@23164
  1315
  apply (subgoal_tac "n * k < n * 1")
wenzelm@23164
  1316
   apply (drule mult_less_cancel_left [THEN iffD1], auto)
wenzelm@23164
  1317
  done
haftmann@27651
  1318
wenzelm@23164
  1319
lemma zmult_div_cancel: "(n::int) * (m div n) = m - (m mod n)"
wenzelm@23164
  1320
  using zmod_zdiv_equality[where a="m" and b="n"]
nipkow@23477
  1321
  by (simp add: ring_simps)
wenzelm@23164
  1322
wenzelm@23164
  1323
lemma zdvd_mult_div_cancel:"(n::int) dvd m \<Longrightarrow> n * (m div n) = m"
wenzelm@23164
  1324
apply (subgoal_tac "m mod n = 0")
wenzelm@23164
  1325
 apply (simp add: zmult_div_cancel)
wenzelm@23164
  1326
apply (simp only: zdvd_iff_zmod_eq_0)
wenzelm@23164
  1327
done
wenzelm@23164
  1328
wenzelm@23164
  1329
lemma zdvd_mult_cancel: assumes d:"k * m dvd k * n" and kz:"k \<noteq> (0::int)"
wenzelm@23164
  1330
  shows "m dvd n"
wenzelm@23164
  1331
proof-
wenzelm@23164
  1332
  from d obtain h where h: "k*n = k*m * h" unfolding dvd_def by blast
wenzelm@23164
  1333
  {assume "n \<noteq> m*h" hence "k* n \<noteq> k* (m*h)" using kz by simp
wenzelm@23164
  1334
    with h have False by (simp add: mult_assoc)}
wenzelm@23164
  1335
  hence "n = m * h" by blast
wenzelm@23164
  1336
  thus ?thesis by blast
wenzelm@23164
  1337
qed
wenzelm@23164
  1338
nipkow@23969
  1339
lemma zdvd_zmult_cancel_disj[simp]:
nipkow@23969
  1340
  "(k*m) dvd (k*n) = (k=0 | m dvd (n::int))"
nipkow@23969
  1341
by (auto simp: zdvd_zmult_mono dest: zdvd_mult_cancel)
nipkow@23969
  1342
nipkow@23969
  1343
wenzelm@23164
  1344
theorem ex_nat: "(\<exists>x::nat. P x) = (\<exists>x::int. 0 <= x \<and> P (nat x))"
nipkow@25134
  1345
apply (simp split add: split_nat)
nipkow@25134
  1346
apply (rule iffI)
nipkow@25134
  1347
apply (erule exE)
nipkow@25134
  1348
apply (rule_tac x = "int x" in exI)
nipkow@25134
  1349
apply simp
nipkow@25134
  1350
apply (erule exE)
nipkow@25134
  1351
apply (rule_tac x = "nat x" in exI)
nipkow@25134
  1352
apply (erule conjE)
nipkow@25134
  1353
apply (erule_tac x = "nat x" in allE)
nipkow@25134
  1354
apply simp
nipkow@25134
  1355
done
wenzelm@23164
  1356
huffman@23365
  1357
theorem zdvd_int: "(x dvd y) = (int x dvd int y)"
haftmann@27651
  1358
proof -
haftmann@27651
  1359
  have "\<And>k. int y = int x * k \<Longrightarrow> x dvd y"
haftmann@27651
  1360
  proof -
haftmann@27651
  1361
    fix k
haftmann@27651
  1362
    assume A: "int y = int x * k"
haftmann@27651
  1363
    then show "x dvd y" proof (cases k)
haftmann@27651
  1364
      case (1 n) with A have "y = x * n" by (simp add: zmult_int)
haftmann@27651
  1365
      then show ?thesis ..
haftmann@27651
  1366
    next
haftmann@27651
  1367
      case (2 n) with A have "int y = int x * (- int (Suc n))" by simp
haftmann@27651
  1368
      also have "\<dots> = - (int x * int (Suc n))" by (simp only: mult_minus_right)
haftmann@27651
  1369
      also have "\<dots> = - int (x * Suc n)" by (simp only: zmult_int)
haftmann@27651
  1370
      finally have "- int (x * Suc n) = int y" ..
haftmann@27651
  1371
      then show ?thesis by (simp only: negative_eq_positive) auto
haftmann@27651
  1372
    qed
haftmann@27651
  1373
  qed
haftmann@27651
  1374
  then show ?thesis by (auto elim!: dvdE simp only: zmult_int [symmetric])
haftmann@27651
  1375
qed 
wenzelm@23164
  1376
wenzelm@23164
  1377
lemma zdvd1_eq[simp]: "(x::int) dvd 1 = ( \<bar>x\<bar> = 1)"
wenzelm@23164
  1378
proof
wenzelm@23164
  1379
  assume d: "x dvd 1" hence "int (nat \<bar>x\<bar>) dvd int (nat 1)" by (simp add: zdvd_abs1)
wenzelm@23164
  1380
  hence "nat \<bar>x\<bar> dvd 1" by (simp add: zdvd_int)
wenzelm@23164
  1381
  hence "nat \<bar>x\<bar> = 1"  by simp
wenzelm@23164
  1382
  thus "\<bar>x\<bar> = 1" by (cases "x < 0", auto)
wenzelm@23164
  1383
next
wenzelm@23164
  1384
  assume "\<bar>x\<bar>=1" thus "x dvd 1" 
wenzelm@23164
  1385
    by(cases "x < 0",simp_all add: minus_equation_iff zdvd_iff_zmod_eq_0)
wenzelm@23164
  1386
qed
wenzelm@23164
  1387
lemma zdvd_mult_cancel1: 
wenzelm@23164
  1388
  assumes mp:"m \<noteq>(0::int)" shows "(m * n dvd m) = (\<bar>n\<bar> = 1)"
wenzelm@23164
  1389
proof
wenzelm@23164
  1390
  assume n1: "\<bar>n\<bar> = 1" thus "m * n dvd m" 
wenzelm@23164
  1391
    by (cases "n >0", auto simp add: zdvd_zminus2_iff minus_equation_iff)
wenzelm@23164
  1392
next
wenzelm@23164
  1393
  assume H: "m * n dvd m" hence H2: "m * n dvd m * 1" by simp
wenzelm@23164
  1394
  from zdvd_mult_cancel[OF H2 mp] show "\<bar>n\<bar> = 1" by (simp only: zdvd1_eq)
wenzelm@23164
  1395
qed
wenzelm@23164
  1396
huffman@23365
  1397
lemma int_dvd_iff: "(int m dvd z) = (m dvd nat (abs z))"
haftmann@27651
  1398
  unfolding zdvd_int by (cases "z \<ge> 0") (simp_all add: zdvd_zminus_iff)
huffman@23306
  1399
huffman@23365
  1400
lemma dvd_int_iff: "(z dvd int m) = (nat (abs z) dvd m)"
haftmann@27651
  1401
  unfolding zdvd_int by (cases "z \<ge> 0") (simp_all add: zdvd_zminus2_iff)
wenzelm@23164
  1402
wenzelm@23164
  1403
lemma nat_dvd_iff: "(nat z dvd m) = (if 0 \<le> z then (z dvd int m) else m = 0)"
haftmann@27651
  1404
  by (auto simp add: dvd_int_iff)
wenzelm@23164
  1405
wenzelm@23164
  1406
lemma zminus_dvd_iff [iff]: "(-z dvd w) = (z dvd (w::int))"
haftmann@27651
  1407
  by (simp add: zdvd_zminus2_iff)
wenzelm@23164
  1408
wenzelm@23164
  1409
lemma dvd_zminus_iff [iff]: "(z dvd -w) = (z dvd (w::int))"
haftmann@27651
  1410
  by (simp add: zdvd_zminus_iff)
wenzelm@23164
  1411
wenzelm@23164
  1412
lemma zdvd_imp_le: "[| z dvd n; 0 < n |] ==> z \<le> (n::int)"
huffman@23365
  1413
  apply (rule_tac z=n in int_cases)
huffman@23365
  1414
  apply (auto simp add: dvd_int_iff)
huffman@23365
  1415
  apply (rule_tac z=z in int_cases)
huffman@23307
  1416
  apply (auto simp add: dvd_imp_le)
wenzelm@23164
  1417
  done
wenzelm@23164
  1418
wenzelm@23164
  1419
lemma zpower_zmod: "((x::int) mod m)^y mod m = x^y mod m"
wenzelm@23164
  1420
apply (induct "y", auto)
wenzelm@23164
  1421
apply (rule zmod_zmult1_eq [THEN trans])
wenzelm@23164
  1422
apply (simp (no_asm_simp))
wenzelm@23164
  1423
apply (rule zmod_zmult_distrib [symmetric])
wenzelm@23164
  1424
done
wenzelm@23164
  1425
huffman@23365
  1426
lemma zdiv_int: "int (a div b) = (int a) div (int b)"
wenzelm@23164
  1427
apply (subst split_div, auto)
wenzelm@23164
  1428
apply (subst split_zdiv, auto)
huffman@23365
  1429
apply (rule_tac a="int (b * i) + int j" and b="int b" and r="int j" and r'=ja in IntDiv.unique_quotient)
huffman@23431
  1430
apply (auto simp add: IntDiv.quorem_def of_nat_mult)
wenzelm@23164
  1431
done
wenzelm@23164
  1432
wenzelm@23164
  1433
lemma zmod_int: "int (a mod b) = (int a) mod (int b)"
huffman@23365
  1434
apply (subst split_mod, auto)
huffman@23365
  1435
apply (subst split_zmod, auto)
huffman@23365
  1436
apply (rule_tac a="int (b * i) + int j" and b="int b" and q="int i" and q'=ia 
huffman@23365
  1437
       in unique_remainder)
huffman@23431
  1438
apply (auto simp add: IntDiv.quorem_def of_nat_mult)
huffman@23365
  1439
done
wenzelm@23164
  1440
wenzelm@23164
  1441
text{*Suggested by Matthias Daum*}
wenzelm@23164
  1442
lemma int_power_div_base:
wenzelm@23164
  1443
     "\<lbrakk>0 < m; 0 < k\<rbrakk> \<Longrightarrow> k ^ m div k = (k::int) ^ (m - Suc 0)"
wenzelm@23164
  1444
apply (subgoal_tac "k ^ m = k ^ ((m - 1) + 1)")
wenzelm@23164
  1445
 apply (erule ssubst)
wenzelm@23164
  1446
 apply (simp only: power_add)
wenzelm@23164
  1447
 apply simp_all
wenzelm@23164
  1448
done
wenzelm@23164
  1449
haftmann@23853
  1450
text {* by Brian Huffman *}
haftmann@23853
  1451
lemma zminus_zmod: "- ((x::int) mod m) mod m = - x mod m"
haftmann@23853
  1452
by (simp only: zmod_zminus1_eq_if mod_mod_trivial)
haftmann@23853
  1453
haftmann@23853
  1454
lemma zdiff_zmod_left: "(x mod m - y) mod m = (x - y) mod (m::int)"
haftmann@23853
  1455
by (simp only: diff_def zmod_zadd_left_eq [symmetric])
haftmann@23853
  1456
haftmann@23853
  1457
lemma zdiff_zmod_right: "(x - y mod m) mod m = (x - y) mod (m::int)"
haftmann@23853
  1458
proof -
haftmann@23853
  1459
  have "(x + - (y mod m) mod m) mod m = (x + - y mod m) mod m"
haftmann@23853
  1460
    by (simp only: zminus_zmod)
haftmann@23853
  1461
  hence "(x + - (y mod m)) mod m = (x + - y) mod m"
haftmann@23853
  1462
    by (simp only: zmod_zadd_right_eq [symmetric])
haftmann@23853
  1463
  thus "(x - y mod m) mod m = (x - y) mod m"
haftmann@23853
  1464
    by (simp only: diff_def)
haftmann@23853
  1465
qed
haftmann@23853
  1466
haftmann@23853
  1467
lemmas zmod_simps =
haftmann@23853
  1468
  IntDiv.zmod_zadd_left_eq  [symmetric]
haftmann@23853
  1469
  IntDiv.zmod_zadd_right_eq [symmetric]
haftmann@23853
  1470
  IntDiv.zmod_zmult1_eq     [symmetric]
haftmann@23853
  1471
  IntDiv.zmod_zmult1_eq'    [symmetric]
haftmann@23853
  1472
  IntDiv.zpower_zmod
haftmann@23853
  1473
  zminus_zmod zdiff_zmod_left zdiff_zmod_right
haftmann@23853
  1474
haftmann@23853
  1475
text {* code generator setup *}
wenzelm@23164
  1476
haftmann@26507
  1477
context ring_1
haftmann@26507
  1478
begin
haftmann@26507
  1479
haftmann@26507
  1480
lemma of_int_num [code func]:
haftmann@26507
  1481
  "of_int k = (if k = 0 then 0 else if k < 0 then
haftmann@26507
  1482
     - of_int (- k) else let
haftmann@26507
  1483
       (l, m) = divAlg (k, 2);
haftmann@26507
  1484
       l' = of_int l
haftmann@26507
  1485
     in if m = 0 then l' + l' else l' + l' + 1)"
haftmann@26507
  1486
proof -
haftmann@26507
  1487
  have aux1: "k mod (2\<Colon>int) \<noteq> (0\<Colon>int) \<Longrightarrow> 
haftmann@26507
  1488
    of_int k = of_int (k div 2 * 2 + 1)"
haftmann@26507
  1489
  proof -
haftmann@26507
  1490
    have "k mod 2 < 2" by (auto intro: pos_mod_bound)
haftmann@26507
  1491
    moreover have "0 \<le> k mod 2" by (auto intro: pos_mod_sign)
haftmann@26507
  1492
    moreover assume "k mod 2 \<noteq> 0"
haftmann@26507
  1493
    ultimately have "k mod 2 = 1" by arith
haftmann@26507
  1494
    moreover have "of_int k = of_int (k div 2 * 2 + k mod 2)" by simp
haftmann@26507
  1495
    ultimately show ?thesis by auto
haftmann@26507
  1496
  qed
haftmann@26507
  1497
  have aux2: "\<And>x. of_int 2 * x = x + x"
haftmann@26507
  1498
  proof -
haftmann@26507
  1499
    fix x
haftmann@26507
  1500
    have int2: "(2::int) = 1 + 1" by arith
haftmann@26507
  1501
    show "of_int 2 * x = x + x"
haftmann@26507
  1502
    unfolding int2 of_int_add left_distrib by simp
haftmann@26507
  1503
  qed
haftmann@26507
  1504
  have aux3: "\<And>x. x * of_int 2 = x + x"
haftmann@26507
  1505
  proof -
haftmann@26507
  1506
    fix x
haftmann@26507
  1507
    have int2: "(2::int) = 1 + 1" by arith
haftmann@26507
  1508
    show "x * of_int 2 = x + x" 
haftmann@26507
  1509
    unfolding int2 of_int_add right_distrib by simp
haftmann@26507
  1510
  qed
haftmann@26507
  1511
  from aux1 show ?thesis by (auto simp add: divAlg_mod_div Let_def aux2 aux3)
haftmann@26507
  1512
qed
haftmann@26507
  1513
haftmann@26507
  1514
end
haftmann@26507
  1515
chaieb@27667
  1516
lemma zmod_eq_dvd_iff: "(x::int) mod n = y mod n \<longleftrightarrow> n dvd x - y"
chaieb@27667
  1517
proof
chaieb@27667
  1518
  assume H: "x mod n = y mod n"
chaieb@27667
  1519
  hence "x mod n - y mod n = 0" by simp
chaieb@27667
  1520
  hence "(x mod n - y mod n) mod n = 0" by simp 
chaieb@27667
  1521
  hence "(x - y) mod n = 0" by (simp add: zmod_zdiff1_eq[symmetric])
chaieb@27667
  1522
  thus "n dvd x - y" by (simp add: zdvd_iff_zmod_eq_0)
chaieb@27667
  1523
next
chaieb@27667
  1524
  assume H: "n dvd x - y"
chaieb@27667
  1525
  then obtain k where k: "x-y = n*k" unfolding dvd_def by blast
chaieb@27667
  1526
  hence "x = n*k + y" by simp
chaieb@27667
  1527
  hence "x mod n = (n*k + y) mod n" by simp
chaieb@27667
  1528
  thus "x mod n = y mod n" by (simp add: zmod_zadd_left_eq)
chaieb@27667
  1529
qed
chaieb@27667
  1530
chaieb@27667
  1531
lemma nat_mod_eq_lemma: assumes xyn: "(x::nat) mod n = y  mod n" and xy:"y \<le> x"
chaieb@27667
  1532
  shows "\<exists>q. x = y + n * q"
chaieb@27667
  1533
proof-
chaieb@27667
  1534
  from xy have th: "int x - int y = int (x - y)" by simp 
chaieb@27667
  1535
  from xyn have "int x mod int n = int y mod int n" 
chaieb@27667
  1536
    by (simp add: zmod_int[symmetric])
chaieb@27667
  1537
  hence "int n dvd int x - int y" by (simp only: zmod_eq_dvd_iff[symmetric]) 
chaieb@27667
  1538
  hence "n dvd x - y" by (simp add: th zdvd_int)
chaieb@27667
  1539
  then show ?thesis using xy unfolding dvd_def apply clarsimp apply (rule_tac x="k" in exI) by arith
chaieb@27667
  1540
qed
chaieb@27667
  1541
chaieb@27667
  1542
lemma nat_mod_eq_iff: "(x::nat) mod n = y mod n \<longleftrightarrow> (\<exists>q1 q2. x + n * q1 = y + n * q2)" 
chaieb@27667
  1543
  (is "?lhs = ?rhs")
chaieb@27667
  1544
proof
chaieb@27667
  1545
  assume H: "x mod n = y mod n"
chaieb@27667
  1546
  {assume xy: "x \<le> y"
chaieb@27667
  1547
    from H have th: "y mod n = x mod n" by simp
chaieb@27667
  1548
    from nat_mod_eq_lemma[OF th xy] have ?rhs 
chaieb@27667
  1549
      apply clarify  apply (rule_tac x="q" in exI) by (rule exI[where x="0"], simp)}
chaieb@27667
  1550
  moreover
chaieb@27667
  1551
  {assume xy: "y \<le> x"
chaieb@27667
  1552
    from nat_mod_eq_lemma[OF H xy] have ?rhs 
chaieb@27667
  1553
      apply clarify  apply (rule_tac x="0" in exI) by (rule_tac x="q" in exI, simp)}
chaieb@27667
  1554
  ultimately  show ?rhs using linear[of x y] by blast  
chaieb@27667
  1555
next
chaieb@27667
  1556
  assume ?rhs then obtain q1 q2 where q12: "x + n * q1 = y + n * q2" by blast
chaieb@27667
  1557
  hence "(x + n * q1) mod n = (y + n * q2) mod n" by simp
chaieb@27667
  1558
  thus  ?lhs by simp
chaieb@27667
  1559
qed
chaieb@27667
  1560
wenzelm@23164
  1561
code_modulename SML
wenzelm@23164
  1562
  IntDiv Integer
wenzelm@23164
  1563
wenzelm@23164
  1564
code_modulename OCaml
wenzelm@23164
  1565
  IntDiv Integer
wenzelm@23164
  1566
wenzelm@23164
  1567
code_modulename Haskell
haftmann@24195
  1568
  IntDiv Integer
wenzelm@23164
  1569
wenzelm@23164
  1570
end