author  wenzelm 
Wed, 27 Mar 2013 16:38:25 +0100  
changeset 51553  63327f679cff 
parent 42460  1805c67dc7aa 
child 51717  9e7d1c139569 
permissions  rwrr 
35762  1 
(* Title: Provers/quantifier1.ML 
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Author: Tobias Nipkow 
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Copyright 1997 TU Munich 

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Simplification procedures for turning 

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? x. ... & x = t & ... 

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into ? x. x = t & ... & ... 

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where the `? x. x = t &' in the latter formula must be eliminated 
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by ordinary simplification. 
4319  11 

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and ! x. (... & x = t & ...) > P x 

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into ! x. x = t > (... & ...) > P x 

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where the `!x. x=t >' in the latter formula is eliminated 

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by ordinary simplification. 

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And analogously for t=x, but the eqn is not turned around! 
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NB Simproc is only triggered by "!x. P(x) & P'(x) > Q(x)"; 
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"!x. x=t > P(x)" is covered by the congruence rule for >; 
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"!x. t=x > P(x)" must be taken care of by an ordinary rewrite rule. 
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As must be "? x. t=x & P(x)". 
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And similarly for the bounded quantifiers. 
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Gries etc call this the "1 point rules" 
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The above also works for !x1..xn. and ?x1..xn by moving the defined 
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quantifier inside first, but not for nested bounded quantifiers. 
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For set comprehensions the basic permutations 
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... & x = t & ... > x = t & (... & ...) 
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... & t = x & ... > t = x & (... & ...) 
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are also exported. 
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To avoid looping, NONE is returned if the term cannot be rearranged, 
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esp if x=t/t=x sits at the front already. 
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*) 
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signature QUANTIFIER1_DATA = 

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sig 

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(*abstract syntax*) 

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val dest_eq: term > (term * term) option 
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val dest_conj: term > (term * term) option 

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val dest_imp: term > (term * term) option 

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val conj: term 
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val imp: term 
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(*rules*) 
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val iff_reflection: thm (* P <> Q ==> P == Q *) 

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val iffI: thm 
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val iff_trans: thm 
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val conjI: thm 
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val conjE: thm 

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val impI: thm 
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val mp: thm 

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val exI: thm 

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val exE: thm 

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val uncurry: thm (* P > Q > R ==> P & Q > R *) 
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val iff_allI: thm (* !!x. P x <> Q x ==> (!x. P x) = (!x. Q x) *) 

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val iff_exI: thm (* !!x. P x <> Q x ==> (? x. P x) = (? x. Q x) *) 
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val all_comm: thm (* (!x y. P x y) = (!y x. P x y) *) 
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val ex_comm: thm (* (? x y. P x y) = (? y x. P x y) *) 
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end; 
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signature QUANTIFIER1 = 

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sig 

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val prove_one_point_all_tac: tactic 
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val prove_one_point_ex_tac: tactic 

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val rearrange_all: simpset > cterm > thm option 
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val rearrange_ex: simpset > cterm > thm option 

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val rearrange_ball: tactic > simpset > cterm > thm option 

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val rearrange_bex: tactic > simpset > cterm > thm option 

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val rearrange_Collect: tactic > simpset > cterm > thm option 

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end; 
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functor Quantifier1(Data: QUANTIFIER1_DATA): QUANTIFIER1 = 
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struct 
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(* FIXME: only test! *) 
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fun def xs eq = 
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(case Data.dest_eq eq of 
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SOME (s, t) => 
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let val n = length xs in 
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s = Bound n andalso not (loose_bvar1 (t, n)) orelse 

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t = Bound n andalso not (loose_bvar1 (s, n)) 

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end 

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 NONE => false); 

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fun extract_conj fst xs t = 
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(case Data.dest_conj t of 

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NONE => NONE 

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 SOME (P, Q) => 
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if def xs P then (if fst then NONE else SOME (xs, P, Q)) 
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else if def xs Q then SOME (xs, Q, P) 

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else 

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(case extract_conj false xs P of 

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SOME (xs, eq, P') => SOME (xs, eq, Data.conj $ P' $ Q) 

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 NONE => 

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(case extract_conj false xs Q of 

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SOME (xs, eq, Q') => SOME (xs, eq, Data.conj $ P $ Q') 

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 NONE => NONE))); 

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fun extract_imp fst xs t = 
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(case Data.dest_imp t of 

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NONE => NONE 

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 SOME (P, Q) => 
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if def xs P then (if fst then NONE else SOME (xs, P, Q)) 
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else 

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(case extract_conj false xs P of 

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SOME (xs, eq, P') => SOME (xs, eq, Data.imp $ P' $ Q) 

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 NONE => 

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(case extract_imp false xs Q of 

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NONE => NONE 

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 SOME (xs, eq, Q') => SOME (xs, eq, Data.imp $ P $ Q')))); 

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fun extract_quant extract q = 
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let 
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fun exqu xs ((qC as Const (qa, _)) $ Abs (x, T, Q)) = 
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if qa = q then exqu ((qC, x, T) :: xs) Q else NONE 
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 exqu xs P = extract (null xs) xs P 

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in exqu [] end; 
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fun prove_conv tac ss tu = 
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let 
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val ctxt = Simplifier.the_context ss; 
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val (goal, ctxt') = 
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yield_singleton (Variable.import_terms true) (Logic.mk_equals tu) ctxt; 
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val thm = 
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Goal.prove ctxt' [] [] goal (K (rtac Data.iff_reflection 1 THEN tac)); 
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in singleton (Variable.export ctxt' ctxt) thm end; 
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fun qcomm_tac qcomm qI i = REPEAT_DETERM (rtac qcomm i THEN rtac qI i); 
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(* Proves (? x0..xn. ... & x0 = t & ...) = (? x1..xn x0. x0 = t & ... & ...) 
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Better: instantiate exI 
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*) 

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local 
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val excomm = Data.ex_comm RS Data.iff_trans; 
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in 
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val prove_one_point_ex_tac = 
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qcomm_tac excomm Data.iff_exI 1 THEN rtac Data.iffI 1 THEN 

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ALLGOALS 

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(EVERY' [etac Data.exE, REPEAT_DETERM o etac Data.conjE, rtac Data.exI, 

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DEPTH_SOLVE_1 o ares_tac [Data.conjI]]) 

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end; 
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(* Proves (! x0..xn. (... & x0 = t & ...) > P x0) = 
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(! x1..xn x0. x0 = t > (... & ...) > P x0) 
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*) 
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local 
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val tac = 
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SELECT_GOAL 

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(EVERY1 [REPEAT o dtac Data.uncurry, REPEAT o rtac Data.impI, etac Data.mp, 

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REPEAT o etac Data.conjE, REPEAT o ares_tac [Data.conjI]]); 

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val allcomm = Data.all_comm RS Data.iff_trans; 

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in 
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val prove_one_point_all_tac = 
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EVERY1 [qcomm_tac allcomm Data.iff_allI, rtac Data.iff_allI, rtac Data.iffI, tac, tac]; 

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end 
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fun renumber l u (Bound i) = 
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Bound (if i < l orelse i > u then i else if i = u then l else i + 1) 

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 renumber l u (s $ t) = renumber l u s $ renumber l u t 

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 renumber l u (Abs (x, T, t)) = Abs (x, T, renumber (l + 1) (u + 1) t) 

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 renumber _ _ atom = atom; 
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fun quantify qC x T xs P = 
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let 
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fun quant [] P = P 

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 quant ((qC, x, T) :: xs) P = quant xs (qC $ Abs (x, T, P)); 

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val n = length xs; 

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val Q = if n = 0 then P else renumber 0 n P; 

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in quant xs (qC $ Abs (x, T, Q)) end; 

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fun rearrange_all ss ct = 
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(case term_of ct of 

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F as (all as Const (q, _)) $ Abs (x, T, P) => 

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(case extract_quant extract_imp q P of 
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NONE => NONE 
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 SOME (xs, eq, Q) => 
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let val R = quantify all x T xs (Data.imp $ eq $ Q) 
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in SOME (prove_conv prove_one_point_all_tac ss (F, R)) end) 
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 _ => NONE); 
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fun rearrange_ball tac ss ct = 
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(case term_of ct of 

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F as Ball $ A $ Abs (x, T, P) => 

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(case extract_imp true [] P of 
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NONE => NONE 
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 SOME (xs, eq, Q) => 
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if not (null xs) then NONE 

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else 

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let val R = Data.imp $ eq $ Q 

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in SOME (prove_conv tac ss (F, Ball $ A $ Abs (x, T, R))) end) 

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 _ => NONE); 
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42459  197 
fun rearrange_ex ss ct = 
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(case term_of ct of 

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F as (ex as Const (q, _)) $ Abs (x, T, P) => 

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(case extract_quant extract_conj q P of 
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NONE => NONE 
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 SOME (xs, eq, Q) => 
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let val R = quantify ex x T xs (Data.conj $ eq $ Q) 
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in SOME (prove_conv prove_one_point_ex_tac ss (F, R)) end) 
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 _ => NONE); 
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fun rearrange_bex tac ss ct = 
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(case term_of ct of 

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F as Bex $ A $ Abs (x, T, P) => 

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(case extract_conj true [] P of 
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NONE => NONE 
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 SOME (xs, eq, Q) => 
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if not (null xs) then NONE 

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else SOME (prove_conv tac ss (F, Bex $ A $ Abs (x, T, Data.conj $ eq $ Q)))) 

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 _ => NONE); 
11221  216 

42459  217 
fun rearrange_Collect tac ss ct = 
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(case term_of ct of 

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F as Collect $ Abs (x, T, P) => 

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(case extract_conj true [] P of 
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NONE => NONE 
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 SOME (_, eq, Q) => 
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let val R = Collect $ Abs (x, T, Data.conj $ eq $ Q) 

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in SOME (prove_conv tac ss (F, R)) end) 

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 _ => NONE); 
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4319  227 
end; 
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