author  lcp 
Thu, 30 Sep 1993 10:26:38 +0100  
changeset 15  6c6d2f6e3185 
parent 6  8ce8c4d13d4d 
child 30  d49df4181f0d 
permissions  rwrr 
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(* Title: ZF/nat.ML 
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ID: $Id$ 

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Author: Lawrence C Paulson, Cambridge University Computer Laboratory 

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Copyright 1992 University of Cambridge 

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For nat.thy. Natural numbers in ZermeloFraenkel Set Theory 

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*) 

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open Nat; 

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goal Nat.thy "bnd_mono(Inf, %X. {0} Un {succ(i). i:X})"; 

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by (rtac bnd_monoI 1); 

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by (REPEAT (ares_tac [subset_refl, RepFun_mono, Un_mono] 2)); 

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by (cut_facts_tac [infinity] 1); 

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by (fast_tac ZF_cs 1); 

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val nat_bnd_mono = result(); 

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(* nat = {0} Un {succ(x). x:nat} *) 

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val nat_unfold = nat_bnd_mono RS (nat_def RS def_lfp_Tarski); 

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(** Type checking of 0 and successor **) 

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goal Nat.thy "0 : nat"; 

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by (rtac (nat_unfold RS ssubst) 1); 

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by (rtac (singletonI RS UnI1) 1); 

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val nat_0I = result(); 

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val prems = goal Nat.thy "n : nat ==> succ(n) : nat"; 

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by (rtac (nat_unfold RS ssubst) 1); 

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by (rtac (RepFunI RS UnI2) 1); 

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by (resolve_tac prems 1); 

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val nat_succI = result(); 

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goal Nat.thy "1 : nat"; 
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by (rtac (nat_0I RS nat_succI) 1); 
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val nat_1I = result(); 

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goal Nat.thy "bool <= nat"; 

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by (REPEAT (ares_tac [subsetI,nat_0I,nat_1I] 1 ORELSE etac boolE 1)); 

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val bool_subset_nat = result(); 

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val bool_into_nat = bool_subset_nat RS subsetD; 

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(** Injectivity properties and induction **) 

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(*Mathematical induction*) 

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val major::prems = goal Nat.thy 

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"[ n: nat; P(0); !!x. [ x: nat; P(x) ] ==> P(succ(x)) ] ==> P(n)"; 

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by (rtac ([nat_def, nat_bnd_mono, major] MRS def_induct) 1); 

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by (fast_tac (ZF_cs addIs prems) 1); 

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val nat_induct = result(); 

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(*Perform induction on n, then prove the n:nat subgoal using prems. *) 

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fun nat_ind_tac a prems i = 

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EVERY [res_inst_tac [("n",a)] nat_induct i, 

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rename_last_tac a ["1"] (i+2), 

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ares_tac prems i]; 

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val major::prems = goal Nat.thy 

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"[ n: nat; n=0 ==> P; !!x. [ x: nat; n=succ(x) ] ==> P ] ==> P"; 

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by (rtac (major RS (nat_unfold RS equalityD1 RS subsetD) RS UnE) 1); 
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by (DEPTH_SOLVE (eresolve_tac [singletonE,RepFunE] 1 
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ORELSE ares_tac prems 1)); 

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val natE = result(); 

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val prems = goal Nat.thy "n: nat ==> Ord(n)"; 

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by (nat_ind_tac "n" prems 1); 

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by (REPEAT (ares_tac [Ord_0, Ord_succ] 1)); 

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val naturals_are_ordinals = result(); 

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(* i: nat ==> 0: succ(i) *) 
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val nat_0_in_succ = naturals_are_ordinals RS Ord_0_in_succ; 
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goal Nat.thy "!!n. n: nat ==> n=0  0:n"; 
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by (etac nat_induct 1); 

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by (fast_tac ZF_cs 1); 

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by (fast_tac (ZF_cs addIs [nat_0_in_succ]) 1); 
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val natE0 = result(); 
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goal Nat.thy "Ord(nat)"; 

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by (rtac OrdI 1); 

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by (etac (naturals_are_ordinals RS Ord_is_Transset) 2); 

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by (rewtac Transset_def); 

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by (rtac ballI 1); 

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by (etac nat_induct 1); 

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by (REPEAT (ares_tac [empty_subsetI,succ_subsetI] 1)); 

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val Ord_nat = result(); 

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(* succ(i): nat ==> i: nat *) 
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val succ_natD = [succI1, asm_rl, Ord_nat] MRS Ord_trans; 
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(* [ succ(i): k; k: nat ] ==> i: k *) 
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val succ_in_naturalD = [succI1, asm_rl, naturals_are_ordinals] MRS Ord_trans; 
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(** Variations on mathematical induction **) 
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(*complete induction*) 

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val complete_induct = Ord_nat RSN (2, Ord_induct); 

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val prems = goal Nat.thy 

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"[ m: nat; n: nat; \ 

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\ !!x. [ x: nat; m<=x; P(x) ] ==> P(succ(x)) \ 

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\ ] ==> m <= n > P(m) > P(n)"; 

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by (nat_ind_tac "n" prems 1); 

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by (ALLGOALS 

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(asm_simp_tac 
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(ZF_ss addsimps (prems@distrib_rews@[subset_empty_iff, subset_succ_iff, 
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naturals_are_ordinals])))); 
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val nat_induct_from_lemma = result(); 
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(*Induction starting from m rather than 0*) 

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val prems = goal Nat.thy 

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"[ m <= n; m: nat; n: nat; \ 

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\ P(m); \ 

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\ !!x. [ x: nat; m<=x; P(x) ] ==> P(succ(x)) \ 

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\ ] ==> P(n)"; 

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by (rtac (nat_induct_from_lemma RS mp RS mp) 1); 

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by (REPEAT (ares_tac prems 1)); 

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val nat_induct_from = result(); 

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(*Induction suitable for subtraction and lessthan*) 

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val prems = goal Nat.thy 

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"[ m: nat; n: nat; \ 

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\ !!x. [ x: nat ] ==> P(x,0); \ 

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\ !!y. [ y: nat ] ==> P(0,succ(y)); \ 

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\ !!x y. [ x: nat; y: nat; P(x,y) ] ==> P(succ(x),succ(y)) \ 

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\ ] ==> P(m,n)"; 

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by (res_inst_tac [("x","m")] bspec 1); 

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by (resolve_tac prems 2); 

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by (nat_ind_tac "n" prems 1); 

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by (rtac ballI 2); 

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by (nat_ind_tac "x" [] 2); 

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by (REPEAT (ares_tac (prems@[ballI]) 1 ORELSE etac bspec 1)); 

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val diff_induct = result(); 

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(** Induction principle analogous to trancl_induct **) 
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goal Nat.thy 
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"!!m. m: nat ==> P(m,succ(m)) > (ALL x: nat. P(m,x) > P(m,succ(x))) > \ 
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\ (ALL n:nat. m:n > P(m,n))"; 
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by (etac nat_induct 1); 
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by (ALLGOALS 
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(EVERY' [rtac (impI RS impI), rtac (nat_induct RS ballI), assume_tac, 
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fast_tac ZF_cs, fast_tac ZF_cs])); 
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val succ_less_induct_lemma = result(); 
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val prems = goal Nat.thy 
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"[ m: n; n: nat; \ 
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\ P(m,succ(m)); \ 
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\ !!x. [ x: nat; P(m,x) ] ==> P(m,succ(x)) \ 
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\ ] ==> P(m,n)"; 
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by (res_inst_tac [("P4","P")] 
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(succ_less_induct_lemma RS mp RS mp RS bspec RS mp) 1); 
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by (rtac (Ord_nat RSN (3,Ord_trans)) 1); 
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by (REPEAT (ares_tac (prems @ [ballI,impI]) 1)); 
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val succ_less_induct = result(); 
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(** nat_case **) 
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goalw Nat.thy [nat_case_def] "nat_case(a,b,0) = a"; 
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by (fast_tac (ZF_cs addIs [the_equality]) 1); 
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val nat_case_0 = result(); 

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goalw Nat.thy [nat_case_def] "nat_case(a,b,succ(m)) = b(m)"; 
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by (fast_tac (ZF_cs addIs [the_equality]) 1); 
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val nat_case_succ = result(); 

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val major::prems = goal Nat.thy 

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"[ n: nat; a: C(0); !!m. m: nat ==> b(m): C(succ(m)) \ 

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\ ] ==> nat_case(a,b,n) : C(n)"; 
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by (rtac (major RS nat_induct) 1); 
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by (REPEAT (resolve_tac [nat_case_0 RS ssubst, 

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nat_case_succ RS ssubst] 1 

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THEN resolve_tac prems 1)); 

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by (assume_tac 1); 

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val nat_case_type = result(); 

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(** nat_rec  used to define eclose and transrec, then obsolete **) 

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val nat_rec_trans = wf_Memrel RS (nat_rec_def RS def_wfrec RS trans); 

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goal Nat.thy "nat_rec(0,a,b) = a"; 

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by (rtac nat_rec_trans 1); 

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by (rtac nat_case_0 1); 

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val nat_rec_0 = result(); 

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val [prem] = goal Nat.thy 

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"m: nat ==> nat_rec(succ(m),a,b) = b(m, nat_rec(m,a,b))"; 

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by (rtac nat_rec_trans 1); 

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by (simp_tac (ZF_ss addsimps [prem, nat_case_succ, nat_succI, Memrel_iff, 
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vimage_singleton_iff]) 1); 
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val nat_rec_succ = result(); 
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(** The union of two natural numbers is a natural number  their maximum **) 

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(* [ i : nat; j : nat ] ==> i Un j : nat *) 
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val Un_nat_type = standard (Ord_nat RSN (3,Ord_member_UnI)); 
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(* [ i : nat; j : nat ] ==> i Int j : nat *) 
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val Int_nat_type = standard (Ord_nat RSN (3,Ord_member_IntI)); 
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