author  berghofe 
Fri, 24 Jul 1998 13:39:47 +0200  
changeset 5191  8ceaa19f7717 
parent 3120  c58423c20740 
child 5977  9f0c8869cf71 
permissions  rwrr 
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(* Title: HOL/LList.thy 
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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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The "filter" functional for coinductive lists 
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defined by a combination of induction and coinduction 
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*) 
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LFilter = LList + Relation + 
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consts 
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findRel :: "('a => bool) => ('a llist * 'a llist)set" 
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inductive "findRel p" 
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intrs 
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found "p x ==> (LCons x l, LCons x l) : findRel p" 
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seek "[ ~p x; (l,l') : findRel p ] ==> (LCons x l, l') : findRel p" 
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constdefs 
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find :: ['a => bool, 'a llist] => 'a llist 
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"find p l == @l'. (l,l'): findRel p  (l' = LNil & l ~: Domain(findRel p))" 
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lfilter :: ['a => bool, 'a llist] => 'a llist 
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"lfilter p l == llist_corec l (%l. case find p l of 
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LNil => Inl () 
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 LCons y z => Inr(y,z))" 
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end 