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(* Title: HOL/arith.ML
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ID: $Id$
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Author: Lawrence C Paulson, Cambridge University Computer Laboratory
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Copyright 1993 University of Cambridge
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For HOL/arith.thy.
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Proofs about elementary arithmetic: addition, multiplication, etc.
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Tests definitions and simplifier.
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*)
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open Arith;
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(*** Basic rewrite rules for the arithmetic operators ***)
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val [pred_0, pred_Suc] = nat_recs pred_def;
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val [add_0,add_Suc] = nat_recs add_def;
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val [mult_0,mult_Suc] = nat_recs mult_def;
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(** Difference **)
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val diff_0 = diff_def RS def_nat_rec_0;
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val diff_0_eq_0 = prove_goalw Arith.thy [diff_def] "0 - n = 0"
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(fn _ => [nat_ind_tac "n" 1, ALLGOALS(asm_simp_tac nat_ss)]);
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(*Must simplify BEFORE the induction!! (Else we get a critical pair)
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Suc(m) - Suc(n) rewrites to pred(Suc(m) - n) *)
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val diff_Suc_Suc = prove_goalw Arith.thy [diff_def] "Suc(m) - Suc(n) = m - n"
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(fn _ =>
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[simp_tac nat_ss 1, nat_ind_tac "n" 1, ALLGOALS(asm_simp_tac nat_ss)]);
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(*** Simplification over add, mult, diff ***)
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val arith_simps =
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[pred_0, pred_Suc, add_0, add_Suc, mult_0, mult_Suc,
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diff_0, diff_0_eq_0, diff_Suc_Suc];
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val arith_ss = nat_ss addsimps arith_simps;
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(**** Inductive properties of the operators ****)
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(*** Addition ***)
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val add_0_right = prove_goal Arith.thy "m + 0 = m"
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(fn _ => [nat_ind_tac "m" 1, ALLGOALS(asm_simp_tac arith_ss)]);
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val add_Suc_right = prove_goal Arith.thy "m + Suc(n) = Suc(m+n)"
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(fn _ => [nat_ind_tac "m" 1, ALLGOALS(asm_simp_tac arith_ss)]);
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val arith_ss = arith_ss addsimps [add_0_right,add_Suc_right];
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(*Associative law for addition*)
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val add_assoc = prove_goal Arith.thy "(m + n) + k = m + (n + k)::nat"
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(fn _ => [nat_ind_tac "m" 1, ALLGOALS(asm_simp_tac arith_ss)]);
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(*Commutative law for addition*)
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val add_commute = prove_goal Arith.thy "m + n = n + m::nat"
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(fn _ => [nat_ind_tac "m" 1, ALLGOALS(asm_simp_tac arith_ss)]);
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val add_left_commute = prove_goal Arith.thy "x+(y+z)=y+(x+z)::nat"
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(fn _ => [rtac trans 1, rtac add_commute 1, rtac trans 1,
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rtac add_assoc 1, rtac (add_commute RS arg_cong) 1]);
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val add_ac = [add_assoc, add_commute, add_left_commute];
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(*** Multiplication ***)
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(*right annihilation in product*)
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val mult_0_right = prove_goal Arith.thy "m * 0 = 0"
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(fn _ => [nat_ind_tac "m" 1, ALLGOALS(asm_simp_tac arith_ss)]);
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(*right Sucessor law for multiplication*)
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val mult_Suc_right = prove_goal Arith.thy "m * Suc(n) = m + (m * n)"
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(fn _ => [nat_ind_tac "m" 1,
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ALLGOALS(asm_simp_tac (arith_ss addsimps add_ac))]);
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val arith_ss = arith_ss addsimps [mult_0_right,mult_Suc_right];
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(*Commutative law for multiplication*)
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val mult_commute = prove_goal Arith.thy "m * n = n * m::nat"
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(fn _ => [nat_ind_tac "m" 1, ALLGOALS (asm_simp_tac arith_ss)]);
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(*addition distributes over multiplication*)
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val add_mult_distrib = prove_goal Arith.thy "(m + n)*k = (m*k) + (n*k)::nat"
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(fn _ => [nat_ind_tac "m" 1,
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ALLGOALS(asm_simp_tac (arith_ss addsimps add_ac))]);
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(*addition distributes over multiplication*)
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val add_mult_distrib = prove_goal Arith.thy "(m + n)*k = (m*k) + (n*k)::nat"
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(fn _ => [nat_ind_tac "m" 1,
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ALLGOALS(asm_simp_tac (arith_ss addsimps add_ac))]);
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val add_mult_distrib2 = prove_goal Arith.thy "k*(m + n) = (k*m) + (k*n)::nat"
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(fn _ => [nat_ind_tac "m" 1,
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ALLGOALS(asm_simp_tac (arith_ss addsimps add_ac))]);
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val arith_ss = arith_ss addsimps [add_mult_distrib,add_mult_distrib2];
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(*Associative law for multiplication*)
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val mult_assoc = prove_goal Arith.thy "(m * n) * k = m * (n * k)::nat"
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(fn _ => [nat_ind_tac "m" 1, ALLGOALS(asm_simp_tac arith_ss)]);
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val mult_left_commute = prove_goal Arith.thy "x*(y*z) = y*(x*z)::nat"
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(fn _ => [rtac trans 1, rtac mult_commute 1, rtac trans 1,
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rtac mult_assoc 1, rtac (mult_commute RS arg_cong) 1]);
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val mult_ac = [mult_assoc,mult_commute,mult_left_commute];
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(*** Difference ***)
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val diff_self_eq_0 = prove_goal Arith.thy "m - m = 0"
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(fn _ => [nat_ind_tac "m" 1, ALLGOALS(asm_simp_tac arith_ss)]);
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(*Addition is the inverse of subtraction: if n<=m then n+(m-n) = m. *)
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val [prem] = goal Arith.thy "[| ~ m<n |] ==> n+(m-n) = m::nat";
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by (rtac (prem RS rev_mp) 1);
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by (res_inst_tac [("m","m"),("n","n")] diff_induct 1);
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by (ALLGOALS(asm_simp_tac arith_ss));
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val add_diff_inverse = result();
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(*** Remainder ***)
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goal Arith.thy "m - n < Suc(m)";
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by (res_inst_tac [("m","m"),("n","n")] diff_induct 1);
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by (etac less_SucE 3);
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by (ALLGOALS(asm_simp_tac arith_ss));
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val diff_less_Suc = result();
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(*In ordinary notation: if 0<n and n<=m then m-n < m *)
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goal Arith.thy "!!m. [| 0<n; ~ m<n |] ==> m - n < m";
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by (subgoal_tac "0<n --> ~ m<n --> m - n < m" 1);
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by (fast_tac HOL_cs 1);
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by (res_inst_tac [("m","m"),("n","n")] diff_induct 1);
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by (ALLGOALS(asm_simp_tac(arith_ss addsimps [diff_less_Suc])));
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val div_termination = result();
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val wf_less_trans = wf_pred_nat RS wf_trancl RSN (2, def_wfrec RS trans);
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goalw Nat.thy [less_def] "<m,n> : pred_nat^+ = (m<n)";
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by (rtac refl 1);
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val less_eq = result();
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goal Arith.thy "!!m. m<n ==> m mod n = m";
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by (rtac (mod_def RS wf_less_trans) 1);
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by(asm_simp_tac HOL_ss 1);
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val mod_less = result();
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goal Arith.thy "!!m. [| 0<n; ~m<n |] ==> m mod n = (m-n) mod n";
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by (rtac (mod_def RS wf_less_trans) 1);
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by(asm_simp_tac (nat_ss addsimps [div_termination, cut_apply, less_eq]) 1);
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val mod_geq = result();
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(*** Quotient ***)
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goal Arith.thy "!!m. m<n ==> m div n = 0";
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by (rtac (div_def RS wf_less_trans) 1);
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by(asm_simp_tac nat_ss 1);
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val div_less = result();
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goal Arith.thy "!!M. [| 0<n; ~m<n |] ==> m div n = Suc((m-n) div n)";
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by (rtac (div_def RS wf_less_trans) 1);
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by(asm_simp_tac (nat_ss addsimps [div_termination, cut_apply, less_eq]) 1);
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val div_geq = result();
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(*Main Result about quotient and remainder.*)
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goal Arith.thy "!!m. 0<n ==> (m div n)*n + m mod n = m";
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by (res_inst_tac [("n","m")] less_induct 1);
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by (rename_tac "k" 1); (*Variable name used in line below*)
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by (case_tac "k<n" 1);
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by (ALLGOALS (asm_simp_tac(arith_ss addsimps (add_ac @
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[mod_less, mod_geq, div_less, div_geq,
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add_diff_inverse, div_termination]))));
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val mod_div_equality = result();
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(*** More results about difference ***)
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val [prem] = goal Arith.thy "m < Suc(n) ==> m-n = 0";
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by (rtac (prem RS rev_mp) 1);
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by (res_inst_tac [("m","m"),("n","n")] diff_induct 1);
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by (ALLGOALS (asm_simp_tac arith_ss));
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val less_imp_diff_is_0 = result();
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val prems = goal Arith.thy "m-n = 0 --> n-m = 0 --> m=n";
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by (res_inst_tac [("m","m"),("n","n")] diff_induct 1);
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by (REPEAT(simp_tac arith_ss 1 THEN TRY(atac 1)));
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val diffs0_imp_equal_lemma = result();
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(* [| m-n = 0; n-m = 0 |] ==> m=n *)
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val diffs0_imp_equal = standard (diffs0_imp_equal_lemma RS mp RS mp);
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val [prem] = goal Arith.thy "m<n ==> 0<n-m";
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by (rtac (prem RS rev_mp) 1);
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by (res_inst_tac [("m","m"),("n","n")] diff_induct 1);
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by (ALLGOALS(asm_simp_tac arith_ss));
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val less_imp_diff_positive = result();
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val [prem] = goal Arith.thy "n < Suc(m) ==> Suc(m)-n = Suc(m-n)";
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by (rtac (prem RS rev_mp) 1);
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by (res_inst_tac [("m","m"),("n","n")] diff_induct 1);
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by (ALLGOALS(asm_simp_tac arith_ss));
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val Suc_diff_n = result();
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goal Arith.thy "Suc(m)-n = if(m<n, 0, Suc(m-n))";
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by(simp_tac (nat_ss addsimps [less_imp_diff_is_0, not_less_eq, Suc_diff_n]
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setloop (split_tac [expand_if])) 1);
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val if_Suc_diff_n = result();
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goal Arith.thy "P(k) --> (!n. P(Suc(n))--> P(n)) --> P(k-i)";
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by (res_inst_tac [("m","k"),("n","i")] diff_induct 1);
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by (ALLGOALS (strip_tac THEN' simp_tac arith_ss THEN' TRY o fast_tac HOL_cs));
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val zero_induct_lemma = result();
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val prems = goal Arith.thy "[| P(k); !!n. P(Suc(n)) ==> P(n) |] ==> P(0)";
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by (rtac (diff_self_eq_0 RS subst) 1);
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by (rtac (zero_induct_lemma RS mp RS mp) 1);
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by (REPEAT (ares_tac ([impI,allI]@prems) 1));
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val zero_induct = result();
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(*13 July 1992: loaded in 105.7s*)
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(**** Additional theorems about "less than" ****)
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goal Arith.thy "n <= (m + n)::nat";
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by (nat_ind_tac "m" 1);
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by (ALLGOALS(simp_tac arith_ss));
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by (etac le_trans 1);
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by (rtac (lessI RS less_imp_le) 1);
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val le_add2 = result();
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goal Arith.thy "n <= (n + m)::nat";
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by (simp_tac (arith_ss addsimps add_ac) 1);
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by (rtac le_add2 1);
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val le_add1 = result();
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val less_add_Suc1 = standard (lessI RS (le_add1 RS le_less_trans));
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val less_add_Suc2 = standard (lessI RS (le_add2 RS le_less_trans));
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goal Arith.thy "m+k<=n --> m<=n::nat";
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by (nat_ind_tac "k" 1);
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by (ALLGOALS (asm_simp_tac arith_ss));
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by (fast_tac (HOL_cs addDs [Suc_leD]) 1);
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val plus_leD1_lemma = result();
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val plus_leD1 = plus_leD1_lemma RS mp;
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