src/HOL/NatDef.ML
author paulson
Thu Sep 23 13:06:31 1999 +0200 (1999-09-23)
changeset 7584 5be4bb8e4e3f
parent 7064 b053e0ab9f60
child 8555 17325ee838ab
permissions -rw-r--r--
tidied; added lemma restrict_to_left
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(*  Title:      HOL/NatDef.ML
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    ID:         $Id$
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    Author:     Tobias Nipkow, Cambridge University Computer Laboratory
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    Copyright   1991  University of Cambridge
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*)
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Goal "mono(%X. {Zero_Rep} Un (Suc_Rep``X))";
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by (REPEAT (ares_tac [monoI, subset_refl, image_mono, Un_mono] 1));
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qed "Nat_fun_mono";
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val Nat_unfold = Nat_fun_mono RS (Nat_def RS def_lfp_Tarski);
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(* Zero is a natural number -- this also justifies the type definition*)
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Goal "Zero_Rep: Nat";
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by (stac Nat_unfold 1);
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by (rtac (singletonI RS UnI1) 1);
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qed "Zero_RepI";
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Goal "i: Nat ==> Suc_Rep(i) : Nat";
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by (stac Nat_unfold 1);
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by (rtac (imageI RS UnI2) 1);
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by (assume_tac 1);
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qed "Suc_RepI";
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(*** Induction ***)
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val major::prems = Goal
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    "[| i: Nat;  P(Zero_Rep);   \
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\       !!j. [| j: Nat; P(j) |] ==> P(Suc_Rep(j)) |]  ==> P(i)";
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by (rtac ([Nat_def, Nat_fun_mono, major] MRS def_induct) 1);
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by (blast_tac (claset() addIs prems) 1);
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qed "Nat_induct";
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val prems = Goalw [Zero_def,Suc_def]
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    "[| P(0);   \
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\       !!n. P(n) ==> P(Suc(n)) |]  ==> P(n)";
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by (rtac (Rep_Nat_inverse RS subst) 1);   (*types force good instantiation*)
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by (rtac (Rep_Nat RS Nat_induct) 1);
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by (REPEAT (ares_tac prems 1
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     ORELSE eresolve_tac [Abs_Nat_inverse RS subst] 1));
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qed "nat_induct";
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(*Perform induction on n. *)
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fun nat_ind_tac a i = 
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  res_inst_tac [("n",a)] nat_induct i  THEN  rename_last_tac a [""] (i+1);
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(*A special form of induction for reasoning about m<n and m-n*)
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val prems = Goal
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    "[| !!x. P x 0;  \
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\       !!y. P 0 (Suc y);  \
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\       !!x y. [| P x y |] ==> P (Suc x) (Suc y)  \
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\    |] ==> P m n";
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by (res_inst_tac [("x","m")] spec 1);
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by (nat_ind_tac "n" 1);
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by (rtac allI 2);
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by (nat_ind_tac "x" 2);
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by (REPEAT (ares_tac (prems@[allI]) 1 ORELSE etac spec 1));
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qed "diff_induct";
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(*** Isomorphisms: Abs_Nat and Rep_Nat ***)
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(*We can't take these properties as axioms, or take Abs_Nat==Inv(Rep_Nat),
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  since we assume the isomorphism equations will one day be given by Isabelle*)
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Goal "inj(Rep_Nat)";
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by (rtac inj_inverseI 1);
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by (rtac Rep_Nat_inverse 1);
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qed "inj_Rep_Nat";
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Goal "inj_on Abs_Nat Nat";
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by (rtac inj_on_inverseI 1);
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by (etac Abs_Nat_inverse 1);
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qed "inj_on_Abs_Nat";
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(*** Distinctness of constructors ***)
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Goalw [Zero_def,Suc_def] "Suc(m) ~= 0";
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by (rtac (inj_on_Abs_Nat RS inj_on_contraD) 1);
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by (rtac Suc_Rep_not_Zero_Rep 1);
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by (REPEAT (resolve_tac [Rep_Nat, Suc_RepI, Zero_RepI] 1));
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qed "Suc_not_Zero";
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bind_thm ("Zero_not_Suc", Suc_not_Zero RS not_sym);
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AddIffs [Suc_not_Zero,Zero_not_Suc];
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bind_thm ("Suc_neq_Zero", (Suc_not_Zero RS notE));
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val Zero_neq_Suc = sym RS Suc_neq_Zero;
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(** Injectiveness of Suc **)
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Goalw [Suc_def] "inj(Suc)";
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by (rtac injI 1);
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by (dtac (inj_on_Abs_Nat RS inj_onD) 1);
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by (REPEAT (resolve_tac [Rep_Nat, Suc_RepI] 1));
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by (dtac (inj_Suc_Rep RS injD) 1);
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by (etac (inj_Rep_Nat RS injD) 1);
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qed "inj_Suc";
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val Suc_inject = inj_Suc RS injD;
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Goal "(Suc(m)=Suc(n)) = (m=n)";
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by (EVERY1 [rtac iffI, etac Suc_inject, etac arg_cong]); 
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qed "Suc_Suc_eq";
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AddIffs [Suc_Suc_eq];
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Goal "n ~= Suc(n)";
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by (nat_ind_tac "n" 1);
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by (ALLGOALS Asm_simp_tac);
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qed "n_not_Suc_n";
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bind_thm ("Suc_n_not_n", n_not_Suc_n RS not_sym);
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(*** Basic properties of "less than" ***)
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Goalw [wf_def, pred_nat_def] "wf(pred_nat)";
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by (Clarify_tac 1);
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by (nat_ind_tac "x" 1);
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by (ALLGOALS Blast_tac);
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qed "wf_pred_nat";
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(*Used in TFL/post.sml*)
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Goalw [less_def] "(m,n) : pred_nat^+ = (m<n)";
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by (rtac refl 1);
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qed "less_eq";
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(** Introduction properties **)
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Goalw [less_def] "[| i<j;  j<k |] ==> i<(k::nat)";
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by (rtac (trans_trancl RS transD) 1);
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by (assume_tac 1);
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by (assume_tac 1);
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qed "less_trans";
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Goalw [less_def, pred_nat_def] "n < Suc(n)";
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by (simp_tac (simpset() addsimps [r_into_trancl]) 1);
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qed "lessI";
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AddIffs [lessI];
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(* i<j ==> i<Suc(j) *)
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bind_thm("less_SucI", lessI RSN (2, less_trans));
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Addsimps [less_SucI];
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Goal "0 < Suc(n)";
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by (nat_ind_tac "n" 1);
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by (rtac lessI 1);
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by (etac less_trans 1);
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by (rtac lessI 1);
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qed "zero_less_Suc";
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AddIffs [zero_less_Suc];
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(** Elimination properties **)
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Goalw [less_def] "n<m ==> ~ m<(n::nat)";
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by (blast_tac (claset() addIs [wf_pred_nat, wf_trancl RS wf_asym])1);
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qed "less_not_sym";
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(* [| n<m; ~P ==> m<n |] ==> P *)
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bind_thm ("less_asym", less_not_sym RS swap);
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Goalw [less_def] "~ n<(n::nat)";
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by (rtac notI 1);
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by (etac (wf_pred_nat RS wf_trancl RS wf_irrefl) 1);
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qed "less_not_refl";
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(* n<n ==> R *)
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bind_thm ("less_irrefl", (less_not_refl RS notE));
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AddSEs [less_irrefl];
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Goal "n<m ==> m ~= (n::nat)";
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by (Blast_tac 1);
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qed "less_not_refl2";
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(* s < t ==> s ~= t *)
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bind_thm ("less_not_refl3", less_not_refl2 RS not_sym);
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val major::prems = Goalw [less_def, pred_nat_def]
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    "[| i<k;  k=Suc(i) ==> P;  !!j. [| i<j;  k=Suc(j) |] ==> P \
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\    |] ==> P";
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by (rtac (major RS tranclE) 1);
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by (ALLGOALS Full_simp_tac); 
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by (REPEAT_FIRST (bound_hyp_subst_tac ORELSE'
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                  eresolve_tac (prems@[asm_rl, Pair_inject])));
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qed "lessE";
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Goal "~ n<0";
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by (rtac notI 1);
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by (etac lessE 1);
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by (etac Zero_neq_Suc 1);
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by (etac Zero_neq_Suc 1);
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qed "not_less0";
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AddIffs [not_less0];
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(* n<0 ==> R *)
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bind_thm ("less_zeroE", not_less0 RS notE);
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val [major,less,eq] = Goal
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    "[| m < Suc(n);  m<n ==> P;  m=n ==> P |] ==> P";
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by (rtac (major RS lessE) 1);
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by (rtac eq 1);
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by (Blast_tac 1);
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by (rtac less 1);
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by (Blast_tac 1);
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qed "less_SucE";
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Goal "(m < Suc(n)) = (m < n | m = n)";
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by (blast_tac (claset() addSEs [less_SucE] addIs [less_trans]) 1);
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qed "less_Suc_eq";
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Goal "(n<1) = (n=0)";
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by (simp_tac (simpset() addsimps [less_Suc_eq]) 1);
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qed "less_one";
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AddIffs [less_one];
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Goal "m<n ==> Suc(m) < Suc(n)";
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by (etac rev_mp 1);
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by (nat_ind_tac "n" 1);
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by (ALLGOALS (fast_tac (claset() addEs [less_trans, lessE])));
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qed "Suc_mono";
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(*"Less than" is a linear ordering*)
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Goal "m<n | m=n | n<(m::nat)";
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by (nat_ind_tac "m" 1);
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by (nat_ind_tac "n" 1);
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by (rtac (refl RS disjI1 RS disjI2) 1);
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by (rtac (zero_less_Suc RS disjI1) 1);
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by (blast_tac (claset() addIs [Suc_mono, less_SucI] addEs [lessE]) 1);
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qed "less_linear";
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Goal "!!m::nat. (m ~= n) = (m<n | n<m)";
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by (cut_facts_tac [less_linear] 1);
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by (Blast_tac 1);
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qed "nat_neq_iff";
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val [major,eqCase,lessCase] = Goal 
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   "[| (m::nat)<n ==> P n m; m=n ==> P n m; n<m ==> P n m |] ==> P n m";
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by (rtac (less_linear RS disjE) 1);
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by (etac disjE 2);
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by (etac lessCase 1);
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by (etac (sym RS eqCase) 1);
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by (etac major 1);
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qed "nat_less_cases";
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(** Inductive (?) properties **)
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Goal "[| m<n; Suc m ~= n |] ==> Suc(m) < n";
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by (full_simp_tac (simpset() addsimps [nat_neq_iff]) 1);
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by (blast_tac (claset() addSEs [less_irrefl, less_SucE] addEs [less_asym]) 1);
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qed "Suc_lessI";
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Goal "Suc(m) < n ==> m<n";
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by (etac rev_mp 1);
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by (nat_ind_tac "n" 1);
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by (ALLGOALS (fast_tac (claset() addSIs [lessI RS less_SucI]
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                                 addEs  [less_trans, lessE])));
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qed "Suc_lessD";
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val [major,minor] = Goal 
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    "[| Suc(i)<k;  !!j. [| i<j;  k=Suc(j) |] ==> P \
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\    |] ==> P";
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by (rtac (major RS lessE) 1);
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by (etac (lessI RS minor) 1);
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by (etac (Suc_lessD RS minor) 1);
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by (assume_tac 1);
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qed "Suc_lessE";
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Goal "Suc(m) < Suc(n) ==> m<n";
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by (blast_tac (claset() addEs [lessE, make_elim Suc_lessD]) 1);
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qed "Suc_less_SucD";
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Goal "(Suc(m) < Suc(n)) = (m<n)";
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by (EVERY1 [rtac iffI, etac Suc_less_SucD, etac Suc_mono]);
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qed "Suc_less_eq";
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Addsimps [Suc_less_eq];
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(*Goal "~(Suc(n) < n)";
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by (blast_tac (claset() addEs [Suc_lessD RS less_irrefl]) 1);
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qed "not_Suc_n_less_n";
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Addsimps [not_Suc_n_less_n];*)
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Goal "i<j ==> j<k --> Suc i < k";
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by (nat_ind_tac "k" 1);
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by (ALLGOALS (asm_simp_tac (simpset())));
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by (asm_simp_tac (simpset() addsimps [less_Suc_eq]) 1);
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by (blast_tac (claset() addDs [Suc_lessD]) 1);
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qed_spec_mp "less_trans_Suc";
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(*Can be used with less_Suc_eq to get n=m | n<m *)
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Goal "(~ m < n) = (n < Suc(m))";
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by (res_inst_tac [("m","m"),("n","n")] diff_induct 1);
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by (ALLGOALS Asm_simp_tac);
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qed "not_less_eq";
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(*Complete induction, aka course-of-values induction*)
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val prems = Goalw [less_def]
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    "[| !!n. [| ! m::nat. m<n --> P(m) |] ==> P(n) |]  ==>  P(n)";
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by (wf_ind_tac "n" [wf_pred_nat RS wf_trancl] 1);
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by (eresolve_tac prems 1);
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qed "less_induct";
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(*** Properties of <= ***)
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(*Was le_eq_less_Suc, but this orientation is more useful*)
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Goalw [le_def] "(m < Suc n) = (m <= n)";
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by (rtac (not_less_eq RS sym) 1);
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qed "less_Suc_eq_le";
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(*  m<=n ==> m < Suc n  *)
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bind_thm ("le_imp_less_Suc", less_Suc_eq_le RS iffD2);
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Goalw [le_def] "0 <= n";
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by (rtac not_less0 1);
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qed "le0";
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AddIffs [le0];
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Goalw [le_def] "~ Suc n <= n";
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by (Simp_tac 1);
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qed "Suc_n_not_le_n";
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Goalw [le_def] "(i <= 0) = (i = 0)";
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   326
by (nat_ind_tac "i" 1);
nipkow@2608
   327
by (ALLGOALS Asm_simp_tac);
nipkow@2608
   328
qed "le_0_eq";
paulson@4614
   329
AddIffs [le_0_eq];
nipkow@2608
   330
paulson@5143
   331
Goal "(m <= Suc(n)) = (m<=n | m = Suc n)";
paulson@5500
   332
by (simp_tac (simpset() delsimps [less_Suc_eq_le]
paulson@5500
   333
			addsimps [less_Suc_eq_le RS sym, less_Suc_eq]) 1);
paulson@3355
   334
qed "le_Suc_eq";
paulson@3355
   335
paulson@4614
   336
(* [| m <= Suc n;  m <= n ==> R;  m = Suc n ==> R |] ==> R *)
paulson@4614
   337
bind_thm ("le_SucE", le_Suc_eq RS iffD1 RS disjE);
paulson@4614
   338
paulson@5316
   339
Goalw [le_def] "~n<m ==> m<=(n::nat)";
paulson@5316
   340
by (assume_tac 1);
nipkow@2608
   341
qed "leI";
nipkow@2608
   342
paulson@5316
   343
Goalw [le_def] "m<=n ==> ~ n < (m::nat)";
paulson@5316
   344
by (assume_tac 1);
nipkow@2608
   345
qed "leD";
nipkow@2608
   346
nipkow@2608
   347
val leE = make_elim leD;
nipkow@2608
   348
wenzelm@5069
   349
Goal "(~n<m) = (m<=(n::nat))";
wenzelm@4089
   350
by (blast_tac (claset() addIs [leI] addEs [leE]) 1);
nipkow@2608
   351
qed "not_less_iff_le";
nipkow@2608
   352
paulson@5143
   353
Goalw [le_def] "~ m <= n ==> n<(m::nat)";
paulson@2891
   354
by (Blast_tac 1);
nipkow@2608
   355
qed "not_leE";
nipkow@2608
   356
wenzelm@5069
   357
Goalw [le_def] "(~n<=m) = (m<(n::nat))";
paulson@4599
   358
by (Simp_tac 1);
paulson@4599
   359
qed "not_le_iff_less";
paulson@4599
   360
paulson@5143
   361
Goalw [le_def] "m < n ==> Suc(m) <= n";
wenzelm@4089
   362
by (simp_tac (simpset() addsimps [less_Suc_eq]) 1);
wenzelm@4089
   363
by (blast_tac (claset() addSEs [less_irrefl,less_asym]) 1);
paulson@3343
   364
qed "Suc_leI";  (*formerly called lessD*)
nipkow@2608
   365
paulson@5143
   366
Goalw [le_def] "Suc(m) <= n ==> m <= n";
wenzelm@4089
   367
by (asm_full_simp_tac (simpset() addsimps [less_Suc_eq]) 1);
nipkow@2608
   368
qed "Suc_leD";
nipkow@2608
   369
nipkow@2608
   370
(* stronger version of Suc_leD *)
paulson@5148
   371
Goalw [le_def] "Suc m <= n ==> m < n";
wenzelm@4089
   372
by (asm_full_simp_tac (simpset() addsimps [less_Suc_eq]) 1);
nipkow@2608
   373
by (cut_facts_tac [less_linear] 1);
paulson@2891
   374
by (Blast_tac 1);
nipkow@2608
   375
qed "Suc_le_lessD";
nipkow@2608
   376
wenzelm@5069
   377
Goal "(Suc m <= n) = (m < n)";
wenzelm@4089
   378
by (blast_tac (claset() addIs [Suc_leI, Suc_le_lessD]) 1);
nipkow@2608
   379
qed "Suc_le_eq";
nipkow@2608
   380
paulson@5143
   381
Goalw [le_def] "m <= n ==> m <= Suc n";
wenzelm@4089
   382
by (blast_tac (claset() addDs [Suc_lessD]) 1);
nipkow@2608
   383
qed "le_SucI";
nipkow@2608
   384
Addsimps[le_SucI];
nipkow@2608
   385
nipkow@6109
   386
(*bind_thm ("le_Suc", not_Suc_n_less_n RS leI);*)
nipkow@2608
   387
paulson@5143
   388
Goalw [le_def] "m < n ==> m <= (n::nat)";
wenzelm@4089
   389
by (blast_tac (claset() addEs [less_asym]) 1);
nipkow@2608
   390
qed "less_imp_le";
nipkow@2608
   391
paulson@5591
   392
(*For instance, (Suc m < Suc n)  =   (Suc m <= n)  =  (m<n) *)
paulson@5591
   393
val le_simps = [less_imp_le, less_Suc_eq_le, Suc_le_eq];
paulson@5591
   394
paulson@5354
   395
paulson@3343
   396
(** Equivalence of m<=n and  m<n | m=n **)
paulson@3343
   397
paulson@5143
   398
Goalw [le_def] "m <= n ==> m < n | m=(n::nat)";
nipkow@2608
   399
by (cut_facts_tac [less_linear] 1);
wenzelm@4089
   400
by (blast_tac (claset() addEs [less_irrefl,less_asym]) 1);
nipkow@2608
   401
qed "le_imp_less_or_eq";
nipkow@2608
   402
paulson@5143
   403
Goalw [le_def] "m<n | m=n ==> m <=(n::nat)";
nipkow@2608
   404
by (cut_facts_tac [less_linear] 1);
wenzelm@4089
   405
by (blast_tac (claset() addSEs [less_irrefl] addEs [less_asym]) 1);
nipkow@2608
   406
qed "less_or_eq_imp_le";
nipkow@2608
   407
wenzelm@5069
   408
Goal "(m <= (n::nat)) = (m < n | m=n)";
nipkow@2608
   409
by (REPEAT(ares_tac [iffI,less_or_eq_imp_le,le_imp_less_or_eq] 1));
nipkow@2608
   410
qed "le_eq_less_or_eq";
nipkow@2608
   411
paulson@4635
   412
(*Useful with Blast_tac.   m=n ==> m<=n *)
paulson@4635
   413
bind_thm ("eq_imp_le", disjI2 RS less_or_eq_imp_le);
paulson@4635
   414
wenzelm@5069
   415
Goal "n <= (n::nat)";
wenzelm@4089
   416
by (simp_tac (simpset() addsimps [le_eq_less_or_eq]) 1);
nipkow@2608
   417
qed "le_refl";
nipkow@2608
   418
paulson@5354
   419
paulson@5143
   420
Goal "[| i <= j; j < k |] ==> i < (k::nat)";
paulson@4468
   421
by (blast_tac (claset() addSDs [le_imp_less_or_eq]
paulson@4468
   422
	                addIs [less_trans]) 1);
nipkow@2608
   423
qed "le_less_trans";
nipkow@2608
   424
paulson@5143
   425
Goal "[| i < j; j <= k |] ==> i < (k::nat)";
paulson@4468
   426
by (blast_tac (claset() addSDs [le_imp_less_or_eq]
paulson@4468
   427
	                addIs [less_trans]) 1);
nipkow@2608
   428
qed "less_le_trans";
nipkow@2608
   429
paulson@5143
   430
Goal "[| i <= j; j <= k |] ==> i <= (k::nat)";
paulson@4468
   431
by (blast_tac (claset() addSDs [le_imp_less_or_eq]
paulson@4468
   432
	                addIs [less_or_eq_imp_le, less_trans]) 1);
nipkow@2608
   433
qed "le_trans";
nipkow@2608
   434
paulson@5143
   435
Goal "[| m <= n; n <= m |] ==> m = (n::nat)";
paulson@4468
   436
(*order_less_irrefl could make this proof fail*)
paulson@4468
   437
by (blast_tac (claset() addSDs [le_imp_less_or_eq]
paulson@4468
   438
	                addSEs [less_irrefl] addEs [less_asym]) 1);
nipkow@2608
   439
qed "le_anti_sym";
nipkow@2608
   440
wenzelm@5069
   441
Goal "(Suc(n) <= Suc(m)) = (n <= m)";
paulson@5500
   442
by (simp_tac (simpset() addsimps le_simps) 1);
nipkow@2608
   443
qed "Suc_le_mono";
nipkow@2608
   444
nipkow@2608
   445
AddIffs [Suc_le_mono];
nipkow@2608
   446
paulson@5500
   447
(* Axiom 'order_less_le' of class 'order': *)
wenzelm@5069
   448
Goal "(m::nat) < n = (m <= n & m ~= n)";
paulson@4737
   449
by (simp_tac (simpset() addsimps [le_def, nat_neq_iff]) 1);
paulson@4737
   450
by (blast_tac (claset() addSEs [less_asym]) 1);
nipkow@2608
   451
qed "nat_less_le";
nipkow@2608
   452
paulson@5354
   453
(* [| m <= n; m ~= n |] ==> m < n *)
paulson@5354
   454
bind_thm ("le_neq_implies_less", [nat_less_le, conjI] MRS iffD2);
paulson@5354
   455
nipkow@4640
   456
(* Axiom 'linorder_linear' of class 'linorder': *)
wenzelm@5069
   457
Goal "(m::nat) <= n | n <= m";
nipkow@4640
   458
by (simp_tac (simpset() addsimps [le_eq_less_or_eq]) 1);
nipkow@4640
   459
by (cut_facts_tac [less_linear] 1);
wenzelm@5132
   460
by (Blast_tac 1);
nipkow@4640
   461
qed "nat_le_linear";
nipkow@4640
   462
paulson@5354
   463
Goal "~ n < m ==> (n < Suc m) = (n = m)";
paulson@5354
   464
by (blast_tac (claset() addSEs [less_SucE]) 1);
paulson@5354
   465
qed "not_less_less_Suc_eq";
paulson@5354
   466
paulson@5354
   467
paulson@5354
   468
(*Rewrite (n < Suc m) to (n=m) if  ~ n<m or m<=n hold.
paulson@5354
   469
  Not suitable as default simprules because they often lead to looping*)
paulson@5354
   470
val not_less_simps = [not_less_less_Suc_eq, leD RS not_less_less_Suc_eq];
nipkow@4640
   471
nipkow@2608
   472
(** LEAST -- the least number operator **)
nipkow@2608
   473
wenzelm@5069
   474
Goal "(! m::nat. P m --> n <= m) = (! m. m < n --> ~ P m)";
wenzelm@4089
   475
by (blast_tac (claset() addIs [leI] addEs [leE]) 1);
nipkow@3143
   476
val lemma = result();
nipkow@3143
   477
nipkow@3143
   478
(* This is an old def of Least for nat, which is derived for compatibility *)
wenzelm@5069
   479
Goalw [Least_def]
nipkow@3143
   480
  "(LEAST n::nat. P n) == (@n. P(n) & (ALL m. m < n --> ~P(m)))";
wenzelm@4089
   481
by (simp_tac (simpset() addsimps [lemma]) 1);
nipkow@3143
   482
qed "Least_nat_def";
nipkow@3143
   483
paulson@5316
   484
val [prem1,prem2] = Goalw [Least_nat_def]
wenzelm@3842
   485
    "[| P(k::nat);  !!x. x<k ==> ~P(x) |] ==> (LEAST x. P(x)) = k";
nipkow@2608
   486
by (rtac select_equality 1);
wenzelm@4089
   487
by (blast_tac (claset() addSIs [prem1,prem2]) 1);
nipkow@2608
   488
by (cut_facts_tac [less_linear] 1);
wenzelm@4089
   489
by (blast_tac (claset() addSIs [prem1] addSDs [prem2]) 1);
nipkow@2608
   490
qed "Least_equality";
nipkow@2608
   491
paulson@5316
   492
Goal "P(k::nat) ==> P(LEAST x. P(x))";
paulson@5316
   493
by (etac rev_mp 1);
nipkow@2608
   494
by (res_inst_tac [("n","k")] less_induct 1);
nipkow@2608
   495
by (rtac impI 1);
nipkow@2608
   496
by (rtac classical 1);
nipkow@2608
   497
by (res_inst_tac [("s","n")] (Least_equality RS ssubst) 1);
nipkow@2608
   498
by (assume_tac 1);
nipkow@2608
   499
by (assume_tac 2);
paulson@2891
   500
by (Blast_tac 1);
nipkow@2608
   501
qed "LeastI";
nipkow@2608
   502
nipkow@2608
   503
(*Proof is almost identical to the one above!*)
paulson@5316
   504
Goal "P(k::nat) ==> (LEAST x. P(x)) <= k";
paulson@5316
   505
by (etac rev_mp 1);
nipkow@2608
   506
by (res_inst_tac [("n","k")] less_induct 1);
nipkow@2608
   507
by (rtac impI 1);
nipkow@2608
   508
by (rtac classical 1);
nipkow@2608
   509
by (res_inst_tac [("s","n")] (Least_equality RS ssubst) 1);
nipkow@2608
   510
by (assume_tac 1);
nipkow@2608
   511
by (rtac le_refl 2);
wenzelm@4089
   512
by (blast_tac (claset() addIs [less_imp_le,le_trans]) 1);
nipkow@2608
   513
qed "Least_le";
nipkow@2608
   514
paulson@5316
   515
Goal "k < (LEAST x. P(x)) ==> ~P(k::nat)";
nipkow@2608
   516
by (rtac notI 1);
paulson@5316
   517
by (etac (rewrite_rule [le_def] Least_le RS notE) 1 THEN assume_tac 1);
nipkow@2608
   518
qed "not_less_Least";
nipkow@2608
   519
nipkow@5983
   520
(* [| m ~= n; m < n ==> P; n < m ==> P |] ==> P *)
paulson@4737
   521
bind_thm("nat_neqE", nat_neq_iff RS iffD1 RS disjE);
nipkow@7064
   522
nipkow@7064
   523
Goal "(S::nat set) ~= {} ==> ? x:S. ! y:S. x <= y";
nipkow@7064
   524
by (cut_facts_tac [wf_pred_nat RS wf_trancl RS (wf_eq_minimal RS iffD1)] 1);
nipkow@7064
   525
by (dres_inst_tac [("x","S")] spec 1);
nipkow@7064
   526
by (Asm_full_simp_tac 1);
nipkow@7064
   527
by (etac impE 1);
nipkow@7064
   528
by (Force_tac 1);
nipkow@7064
   529
by (force_tac (claset(), simpset() addsimps [less_eq,not_le_iff_less]) 1);
nipkow@7064
   530
qed "nonempty_has_least";