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(* Title: FOL/ex/Foundation.ML


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ID: $Id$


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Author: Lawrence C Paulson, Cambridge University Computer Laboratory


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Copyright 1991 University of Cambridge


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*)


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header "Intuitionistic FOL: Examples from The Foundation of a Generic Theorem Prover"


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theory Foundation


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imports IFOL


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begin


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lemma "A&B > (C>A&C)"


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apply (rule impI)


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apply (rule impI)


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apply (rule conjI)


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prefer 2 apply assumption


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apply (rule conjunct1)


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apply assumption


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done


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text {*A form of conjelimination*}


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lemma


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assumes "A & B"


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and "A ==> B ==> C"


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shows C


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apply (rule prems)


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apply (rule conjunct1)


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apply (rule prems)


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apply (rule conjunct2)


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apply (rule prems)


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done


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lemma


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assumes "!!A. ~ ~A ==> A"


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shows "B  ~B"


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apply (rule prems)


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apply (rule notI)


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apply (rule_tac P = "~B" in notE)


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apply (rule_tac [2] notI)


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apply (rule_tac [2] P = "B  ~B" in notE)


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prefer 2 apply assumption


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apply (rule_tac [2] disjI1)


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prefer 2 apply assumption


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apply (rule notI)


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apply (rule_tac P = "B  ~B" in notE)


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apply assumption


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apply (rule disjI2)


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apply assumption


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done


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lemma


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assumes "!!A. ~ ~A ==> A"


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shows "B  ~B"


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apply (rule prems)


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apply (rule notI)


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apply (rule notE)


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apply (rule_tac [2] notI)


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apply (erule_tac [2] notE)


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apply (erule_tac [2] disjI1)


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apply (rule notI)


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apply (erule notE)


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apply (erule disjI2)


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done


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lemma


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assumes "A  ~A"


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and "~ ~A"


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shows A


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apply (rule disjE)


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apply (rule prems)


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apply assumption


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apply (rule FalseE)


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apply (rule_tac P = "~A" in notE)


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apply (rule prems)


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apply assumption


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done


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subsection "Examples with quantifiers"


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lemma


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assumes "ALL z. G(z)"


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shows "ALL z. G(z)H(z)"


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apply (rule allI)


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apply (rule disjI1)


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apply (rule prems [THEN spec])


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done


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lemma "ALL x. EX y. x=y"


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apply (rule allI)


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apply (rule exI)


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apply (rule refl)


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done


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lemma "EX y. ALL x. x=y"


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apply (rule exI)


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apply (rule allI)


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apply (rule refl)?


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oops


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text {* Parallel lifting example. *}


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lemma "EX u. ALL x. EX v. ALL y. EX w. P(u,x,v,y,w)"


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apply (rule exI allI)


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apply (rule exI allI)


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apply (rule exI allI)


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apply (rule exI allI)


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apply (rule exI allI)


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oops


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lemma


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assumes "(EX z. F(z)) & B"


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shows "EX z. F(z) & B"


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apply (rule conjE)


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apply (rule prems)


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apply (rule exE)


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apply assumption


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apply (rule exI)


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apply (rule conjI)


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apply assumption


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apply assumption


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done


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text {* A bigger demonstration of quantifiers  not in the paper. *}


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lemma "(EX y. ALL x. Q(x,y)) > (ALL x. EX y. Q(x,y))"


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apply (rule impI)


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apply (rule allI)


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apply (rule exE, assumption)


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apply (rule exI)


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apply (rule allE, assumption)


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apply assumption


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done


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end
