author | paulson |
Thu, 01 Oct 1998 18:30:05 +0200 | |
changeset 5601 | b6456ccd9e3e |
parent 5599 | 95a92bc7a591 |
child 5983 | 79e301a6a51b |
permissions | -rw-r--r-- |
3335 | 1 |
(* Title: HOL/ex/Primrec |
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ID: $Id$ |
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Author: Lawrence C Paulson, Cambridge University Computer Laboratory |
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Copyright 1997 University of Cambridge |
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Primitive Recursive Functions |
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Proof adopted from |
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Nora Szasz, |
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A Machine Checked Proof that Ackermann's Function is not Primitive Recursive, |
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In: Huet & Plotkin, eds., Logical Environments (CUP, 1993), 317-338. |
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See also E. Mendelson, Introduction to Mathematical Logic. |
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(Van Nostrand, 1964), page 250, exercise 11. |
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*) |
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(** Useful special cases of evaluation ***) |
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Goalw [SC_def] "SC (x#l) = Suc x"; |
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by (Asm_simp_tac 1); |
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qed "SC"; |
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Goalw [CONST_def] "CONST k l = k"; |
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by (Asm_simp_tac 1); |
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qed "CONST"; |
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Goalw [PROJ_def] "PROJ(0) (x#l) = x"; |
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by (Asm_simp_tac 1); |
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qed "PROJ_0"; |
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Goalw [COMP_def] "COMP g [f] l = g [f l]"; |
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by (Asm_simp_tac 1); |
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qed "COMP_1"; |
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Goalw [PREC_def] "PREC f g (0#l) = f l"; |
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by (Asm_simp_tac 1); |
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qed "PREC_0"; |
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Goalw [PREC_def] "PREC f g (Suc x # l) = g (PREC f g (x#l) # x # l)"; |
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by (Asm_simp_tac 1); |
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qed "PREC_Suc"; |
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Addsimps [SC, CONST, PROJ_0, COMP_1, PREC_0, PREC_Suc]; |
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Addsimps ack.rules; |
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(*PROPERTY A 4*) |
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Goal "j < ack(i,j)"; |
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by (res_inst_tac [("u","i"),("v","j")] ack.induct 1); |
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by (ALLGOALS Asm_simp_tac); |
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by (ALLGOALS trans_tac); |
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qed "less_ack2"; |
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AddIffs [less_ack2]; |
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(*PROPERTY A 5-, the single-step lemma*) |
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Goal "ack(i,j) < ack(i, Suc(j))"; |
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by (res_inst_tac [("u","i"),("v","j")] ack.induct 1); |
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by (ALLGOALS Asm_simp_tac); |
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qed "ack_less_ack_Suc2"; |
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AddIffs [ack_less_ack_Suc2]; |
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(*PROPERTY A 5, monotonicity for < *) |
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Goal "j<k --> ack(i,j) < ack(i,k)"; |
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by (res_inst_tac [("u","i"),("v","k")] ack.induct 1); |
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by (ALLGOALS Asm_simp_tac); |
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by (blast_tac (claset() addSEs [less_SucE] addIs [less_trans]) 1); |
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qed_spec_mp "ack_less_mono2"; |
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(*PROPERTY A 5', monotonicity for<=*) |
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Goal "j<=k ==> ack(i,j)<=ack(i,k)"; |
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by (full_simp_tac (simpset() addsimps [order_le_less]) 1); |
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by (blast_tac (claset() addIs [ack_less_mono2]) 1); |
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qed "ack_le_mono2"; |
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(*PROPERTY A 6*) |
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Goal "ack(i, Suc(j)) <= ack(Suc(i), j)"; |
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by (induct_tac "j" 1); |
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by (ALLGOALS Asm_simp_tac); |
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by (blast_tac (claset() addIs [ack_le_mono2, less_ack2 RS Suc_leI, |
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le_trans]) 1); |
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qed "ack2_le_ack1"; |
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AddIffs [ack2_le_ack1]; |
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(*PROPERTY A 7-, the single-step lemma*) |
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Goal "ack(i,j) < ack(Suc(i),j)"; |
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by (blast_tac (claset() addIs [ack_less_mono2, less_le_trans]) 1); |
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qed "ack_less_ack_Suc1"; |
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AddIffs [ack_less_ack_Suc1]; |
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(*PROPERTY A 4'? Extra lemma needed for CONST case, constant functions*) |
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Goal "i < ack(i,j)"; |
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by (induct_tac "i" 1); |
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by (ALLGOALS Asm_simp_tac); |
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by (blast_tac (claset() addIs [Suc_leI, le_less_trans]) 1); |
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qed "less_ack1"; |
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AddIffs [less_ack1]; |
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(*PROPERTY A 8*) |
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Goal "ack(1,j) = Suc(Suc(j))"; |
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by (induct_tac "j" 1); |
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by (ALLGOALS Asm_simp_tac); |
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qed "ack_1"; |
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Addsimps [ack_1]; |
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(*PROPERTY A 9*) |
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Goal "ack(Suc(1),j) = Suc(Suc(Suc(j+j)))"; |
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by (induct_tac "j" 1); |
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by (ALLGOALS Asm_simp_tac); |
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qed "ack_2"; |
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Addsimps [ack_2]; |
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(*PROPERTY A 7, monotonicity for < [not clear why ack_1 is now needed first!]*) |
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Goal "ack(i,k) < ack(Suc(i+i'),k)"; |
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by (res_inst_tac [("u","i"),("v","k")] ack.induct 1); |
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by (ALLGOALS Asm_full_simp_tac); |
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by (blast_tac (claset() addIs [less_trans, ack_less_mono2]) 2); |
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by (res_inst_tac [("u","i'"),("v","n")] ack.induct 1); |
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by (ALLGOALS Asm_simp_tac); |
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by (blast_tac (claset() addIs [less_trans, ack_less_mono2]) 1); |
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by (blast_tac (claset() addIs [Suc_leI RS le_less_trans, ack_less_mono2]) 1); |
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val lemma = result(); |
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Goal "i<j ==> ack(i,k) < ack(j,k)"; |
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by (dtac less_eq_Suc_add 1); |
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by (blast_tac (claset() addSIs [lemma]) 1); |
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qed "ack_less_mono1"; |
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(*PROPERTY A 7', monotonicity for<=*) |
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Goal "i<=j ==> ack(i,k)<=ack(j,k)"; |
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by (full_simp_tac (simpset() addsimps [order_le_less]) 1); |
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by (blast_tac (claset() addIs [ack_less_mono1]) 1); |
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qed "ack_le_mono1"; |
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(*PROPERTY A 10*) |
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Goal "ack(i1, ack(i2,j)) < ack(Suc(Suc(i1+i2)), j)"; |
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by (rtac (ack2_le_ack1 RSN (2,less_le_trans)) 1); |
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by (Asm_simp_tac 1); |
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by (rtac (le_add1 RS ack_le_mono1 RS le_less_trans) 1); |
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by (rtac (ack_less_mono1 RS ack_less_mono2) 1); |
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by (simp_tac (simpset() addsimps [le_imp_less_Suc, le_add2]) 1); |
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qed "ack_nest_bound"; |
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(*PROPERTY A 11*) |
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Goal "ack(i1,j) + ack(i2,j) < ack(Suc(Suc(Suc(Suc(i1+i2)))), j)"; |
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by (res_inst_tac [("j", "ack(Suc(1), ack(i1 + i2, j))")] less_trans 1); |
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by (Asm_simp_tac 1); |
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by (rtac (ack_nest_bound RS less_le_trans) 2); |
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by (Asm_simp_tac 2); |
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by (blast_tac (claset() addSIs [le_add1, le_add2] |
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addIs [le_imp_less_Suc, ack_le_mono1, le_SucI, |
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add_le_mono]) 1); |
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qed "ack_add_bound"; |
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(*PROPERTY A 12. Article uses existential quantifier but the ALF proof |
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used k+4. Quantified version must be nested EX k'. ALL i,j... *) |
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Goal "i < ack(k,j) ==> i+j < ack(Suc(Suc(Suc(Suc(k)))), j)"; |
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by (res_inst_tac [("j", "ack(k,j) + ack(0,j)")] less_trans 1); |
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by (rtac (ack_add_bound RS less_le_trans) 2); |
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by (Asm_simp_tac 2); |
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by (REPEAT (ares_tac ([add_less_mono, less_ack2]) 1)); |
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qed "ack_add_bound2"; |
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(*** Inductive definition of the PR functions ***) |
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(*** MAIN RESULT ***) |
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Goalw [SC_def] "SC l < ack(1, list_add l)"; |
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by (induct_tac "l" 1); |
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by (ALLGOALS (simp_tac (simpset() addsimps [le_add1, le_imp_less_Suc]))); |
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qed "SC_case"; |
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Goal "CONST k l < ack(k, list_add l)"; |
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by (Simp_tac 1); |
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qed "CONST_case"; |
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Goalw [PROJ_def] "ALL i. PROJ i l < ack(0, list_add l)"; |
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by (Simp_tac 1); |
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by (induct_tac "l" 1); |
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by (ALLGOALS Asm_simp_tac); |
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by (rtac allI 1); |
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by (exhaust_tac "i" 1); |
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by (asm_simp_tac (simpset() addsimps [le_add1, le_imp_less_Suc]) 1); |
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by (Asm_simp_tac 1); |
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by (blast_tac (claset() addIs [less_le_trans] |
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addSIs [le_add2]) 1); |
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qed_spec_mp "PROJ_case"; |
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(** COMP case **) |
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Goal "fs : lists(PRIMREC Int {f. EX kf. ALL l. f l < ack(kf, list_add l)}) \ |
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\ ==> EX k. ALL l. list_add (map(%f. f l) fs) < ack(k, list_add l)"; |
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by (etac lists.induct 1); |
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by (res_inst_tac [("x","0")] exI 1 THEN Asm_simp_tac 1); |
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by Safe_tac; |
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by (Asm_simp_tac 1); |
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by (rtac exI 1); |
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by (blast_tac (claset() addIs [add_less_mono, ack_add_bound, less_trans]) 1); |
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qed "COMP_map_lemma"; |
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Goalw [COMP_def] |
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"[| ALL l. g l < ack(kg, list_add l); \ |
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\ fs: lists(PRIMREC Int {f. EX kf. ALL l. f l < ack(kf, list_add l)}) \ |
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\ |] ==> EX k. ALL l. COMP g fs l < ack(k, list_add l)"; |
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by (forward_tac [impOfSubs (Int_lower1 RS lists_mono)] 1); |
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by (etac (COMP_map_lemma RS exE) 1); |
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by (rtac exI 1); |
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by (rtac allI 1); |
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by (REPEAT (dtac spec 1)); |
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by (etac less_trans 1); |
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by (blast_tac (claset() addIs [ack_less_mono2, ack_nest_bound, less_trans]) 1); |
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qed "COMP_case"; |
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(** PREC case **) |
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Goalw [PREC_def] |
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"[| ALL l. f l + list_add l < ack(kf, list_add l); \ |
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\ ALL l. g l + list_add l < ack(kg, list_add l) \ |
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\ |] ==> PREC f g l + list_add l < ack(Suc(kf+kg), list_add l)"; |
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by (exhaust_tac "l" 1); |
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by (ALLGOALS Asm_simp_tac); |
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by (blast_tac (claset() addIs [less_trans]) 1); |
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by (etac ssubst 1); (*get rid of the needless assumption*) |
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by (induct_tac "a" 1); |
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by (ALLGOALS Asm_simp_tac); |
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(*base case*) |
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by (blast_tac (claset() addIs [le_add1 RS le_imp_less_Suc RS ack_less_mono1, |
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less_trans]) 1); |
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(*induction step*) |
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by (rtac (Suc_leI RS le_less_trans) 1); |
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by (rtac (le_refl RS add_le_mono RS le_less_trans) 1); |
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by (etac spec 2); |
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by (asm_simp_tac (simpset() addsimps [le_add2]) 1); |
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(*final part of the simplification*) |
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by (Asm_simp_tac 1); |
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by (rtac (le_add2 RS ack_le_mono1 RS le_less_trans) 1); |
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by (etac ack_less_mono2 1); |
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qed "PREC_case_lemma"; |
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Goal "[| ALL l. f l < ack(kf, list_add l); \ |
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\ ALL l. g l < ack(kg, list_add l) \ |
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\ |] ==> EX k. ALL l. PREC f g l< ack(k, list_add l)"; |
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by (rtac exI 1); |
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by (rtac allI 1); |
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by (rtac ([le_add1, PREC_case_lemma] MRS le_less_trans) 1); |
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by (REPEAT (blast_tac (claset() addIs [ack_add_bound2]) 1)); |
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qed "PREC_case"; |
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Goal "f:PRIMREC ==> EX k. ALL l. f l < ack(k, list_add l)"; |
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by (etac PRIMREC.induct 1); |
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by (ALLGOALS |
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(blast_tac (claset() addIs [SC_case, CONST_case, PROJ_case, COMP_case, |
3335 | 260 |
PREC_case]))); |
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qed "ack_bounds_PRIMREC"; |
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Goal "(%l. case l of [] => 0 | x#l' => ack(x,x)) ~: PRIMREC"; |
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by (rtac notI 1); |
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by (etac (ack_bounds_PRIMREC RS exE) 1); |
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by (rtac less_irrefl 1); |
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by (dres_inst_tac [("x", "[x]")] spec 1); |
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by (Asm_full_simp_tac 1); |
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qed "ack_not_PRIMREC"; |
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