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1 (* Title: HOL/indrule.ML |
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2 ID: $Id$ |
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3 Author: Lawrence C Paulson, Cambridge University Computer Laboratory |
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4 Copyright 1994 University of Cambridge |
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5 |
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6 Induction rule module -- for Inductive/Coinductive Definitions |
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7 |
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8 Proves a strong induction rule and a mutual induction rule |
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9 *) |
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10 |
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11 signature INDRULE = |
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12 sig |
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13 val induct : thm (*main induction rule*) |
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14 val mutual_induct : thm (*mutual induction rule*) |
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15 end; |
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16 |
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17 |
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18 functor Indrule_Fun |
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19 (structure Inductive: sig include INDUCTIVE_ARG INDUCTIVE_I end and |
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20 Intr_elim: INTR_ELIM) : INDRULE = |
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21 struct |
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22 open Logic Ind_Syntax Inductive Intr_elim; |
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23 |
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24 val sign = sign_of thy; |
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25 |
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26 val (Const(_,recT),rec_params) = strip_comb (hd rec_tms); |
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27 |
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28 val elem_type = dest_set (body_type recT); |
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29 val domTs = summands(elem_type); |
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30 val big_rec_name = space_implode "_" rec_names; |
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31 val big_rec_tm = list_comb(Const(big_rec_name,recT), rec_params); |
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32 |
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33 val _ = writeln " Proving the induction rules..."; |
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34 |
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35 (*** Prove the main induction rule ***) |
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36 |
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37 val pred_name = "P"; (*name for predicate variables*) |
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38 |
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39 val big_rec_def::part_rec_defs = Intr_elim.defs; |
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40 |
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41 (*Used to express induction rules: adds induction hypotheses. |
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42 ind_alist = [(rec_tm1,pred1),...] -- associates predicates with rec ops |
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43 prem is a premise of an intr rule*) |
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44 fun add_induct_prem ind_alist (prem as Const("Trueprop",_) $ |
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45 (Const("op :",_)$t$X), iprems) = |
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46 (case gen_assoc (op aconv) (ind_alist, X) of |
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47 Some pred => prem :: mk_tprop (pred $ t) :: iprems |
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48 | None => (*possibly membership in M(rec_tm), for M monotone*) |
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49 let fun mk_sb (rec_tm,pred) = |
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50 (case binder_types (fastype_of pred) of |
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51 [T] => (rec_tm, |
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52 Int_const T $ rec_tm $ (Collect_const T $ pred)) |
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53 | _ => error |
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54 "Bug: add_induct_prem called with non-unary predicate") |
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55 in subst_free (map mk_sb ind_alist) prem :: iprems end) |
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56 | add_induct_prem ind_alist (prem,iprems) = prem :: iprems; |
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57 |
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58 (*Make a premise of the induction rule.*) |
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59 fun induct_prem ind_alist intr = |
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60 let val quantfrees = map dest_Free (term_frees intr \\ rec_params) |
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61 val iprems = foldr (add_induct_prem ind_alist) |
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62 (strip_imp_prems intr,[]) |
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63 val (t,X) = rule_concl intr |
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64 val (Some pred) = gen_assoc (op aconv) (ind_alist, X) |
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65 val concl = mk_tprop (pred $ t) |
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66 in list_all_free (quantfrees, list_implies (iprems,concl)) end |
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67 handle Bind => error"Recursion term not found in conclusion"; |
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68 |
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69 (*Avoids backtracking by delivering the correct premise to each goal*) |
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70 fun ind_tac [] 0 = all_tac |
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71 | ind_tac(prem::prems) i = REPEAT (ares_tac [Part_eqI,prem] i) THEN |
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72 ind_tac prems (i-1); |
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73 |
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74 val pred = Free(pred_name, elem_type --> boolT); |
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75 |
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76 val ind_prems = map (induct_prem (map (rpair pred) rec_tms)) intr_tms; |
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77 |
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78 val quant_induct = |
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79 prove_goalw_cterm part_rec_defs |
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80 (cterm_of sign (list_implies (ind_prems, |
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81 mk_tprop (mk_all_imp(big_rec_tm,pred))))) |
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82 (fn prems => |
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83 [rtac (impI RS allI) 1, |
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84 etac raw_induct 1, |
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85 REPEAT (FIRSTGOAL (eresolve_tac [IntE, CollectE, exE, conjE, disjE, |
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86 ssubst])), |
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87 REPEAT (FIRSTGOAL (eresolve_tac [PartE, CollectE])), |
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88 ind_tac (rev prems) (length prems)]) |
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89 handle e => print_sign_exn sign e; |
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90 |
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91 (*** Prove the simultaneous induction rule ***) |
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92 |
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93 (*Make distinct predicates for each inductive set; |
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94 Cartesian products in domT should nest ONLY to the left! *) |
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95 |
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96 (*Given a recursive set and its domain, return the "split" predicate |
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97 and a conclusion for the simultaneous induction rule*) |
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98 fun mk_predpair (rec_tm,domT) = |
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99 let val rec_name = (#1 o dest_Const o head_of) rec_tm |
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100 val T = factors domT ---> boolT |
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101 val pfree = Free(pred_name ^ "_" ^ rec_name, T) |
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102 val frees = mk_frees "za" (binder_types T) |
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103 val qconcl = |
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104 foldr mk_all (frees, |
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105 imp $ (mk_mem (foldr1 mk_Pair frees, rec_tm)) |
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106 $ (list_comb (pfree,frees))) |
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107 in (ap_split boolT pfree (binder_types T), |
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108 qconcl) |
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109 end; |
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110 |
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111 val (preds,qconcls) = split_list (map mk_predpair (rec_tms~~domTs)); |
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112 |
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113 (*Used to form simultaneous induction lemma*) |
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114 fun mk_rec_imp (rec_tm,pred) = |
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115 imp $ (mk_mem (Bound 0, rec_tm)) $ (pred $ Bound 0); |
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116 |
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117 (*To instantiate the main induction rule*) |
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118 val induct_concl = |
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119 mk_tprop(mk_all_imp(big_rec_tm, |
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120 Abs("z", elem_type, |
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121 fold_bal (app conj) |
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122 (map mk_rec_imp (rec_tms~~preds))))) |
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123 and mutual_induct_concl = mk_tprop(fold_bal (app conj) qconcls); |
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124 |
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125 val lemma = (*makes the link between the two induction rules*) |
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126 prove_goalw_cterm part_rec_defs |
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127 (cterm_of sign (mk_implies (induct_concl,mutual_induct_concl))) |
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128 (fn prems => |
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129 [cut_facts_tac prems 1, |
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130 REPEAT (eresolve_tac [asm_rl, conjE, PartE, mp] 1 |
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131 ORELSE resolve_tac [allI, impI, conjI, Part_eqI] 1 |
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132 ORELSE dresolve_tac [spec, mp, splitD] 1)]) |
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133 handle e => print_sign_exn sign e; |
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134 |
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135 (*Mutual induction follows by freeness of Inl/Inr.*) |
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136 |
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137 (*Removes Collects caused by M-operators in the intro rules*) |
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138 val cmonos = [subset_refl RS Int_Collect_mono] RL monos RLN (2,[rev_subsetD]); |
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139 |
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140 (*Avoids backtracking by delivering the correct premise to each goal*) |
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141 fun mutual_ind_tac [] 0 = all_tac |
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142 | mutual_ind_tac(prem::prems) i = |
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143 SELECT_GOAL |
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144 ((*unpackage and use "prem" in the corresponding place*) |
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145 REPEAT (FIRSTGOAL |
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146 (eresolve_tac ([conjE,mp]@cmonos) ORELSE' |
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147 ares_tac [prem,impI,conjI])) |
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148 (*prove remaining goals by contradiction*) |
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149 THEN rewrite_goals_tac (con_defs@part_rec_defs) |
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150 THEN REPEAT (eresolve_tac (PartE :: sumprod_free_SEs) 1)) |
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151 i THEN mutual_ind_tac prems (i-1); |
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152 |
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153 val mutual_induct_split = |
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154 prove_goalw_cterm [] |
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155 (cterm_of sign |
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156 (list_implies (map (induct_prem (rec_tms~~preds)) intr_tms, |
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157 mutual_induct_concl))) |
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158 (fn prems => |
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159 [rtac (quant_induct RS lemma) 1, |
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160 mutual_ind_tac (rev prems) (length prems)]) |
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161 handle e => print_sign_exn sign e; |
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162 |
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163 (*Attempts to remove all occurrences of split*) |
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164 val split_tac = |
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165 REPEAT (SOMEGOAL (FIRST' [rtac splitI, |
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166 dtac splitD, |
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167 etac splitE, |
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168 bound_hyp_subst_tac])) |
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169 THEN prune_params_tac; |
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170 |
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171 (*strip quantifier*) |
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172 val induct = standard (quant_induct RS spec RSN (2,rev_mp)); |
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173 |
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174 val mutual_induct = rule_by_tactic split_tac mutual_induct_split; |
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175 |
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176 end; |