src/FOLP/ex/Quantifiers_Int.thy
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+(*  Title:      FOLP/ex/Quantifiers_Int.thy
+    ID:         \$Id\$
+    Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
+    Copyright   1991  University of Cambridge
+
+First-Order Logic: quantifier examples (intuitionistic and classical)
+Needs declarations of the theory "thy" and the tactic "tac"
+*)
+
+theory Quantifiers_Int
+imports IFOLP
+begin
+
+lemma "?p : (ALL x y. P(x,y))  -->  (ALL y x. P(x,y))"
+  by (tactic {* IntPr.fast_tac 1 *})
+
+lemma "?p : (EX x y. P(x,y)) --> (EX y x. P(x,y))"
+  by (tactic {* IntPr.fast_tac 1 *})
+
+
+(*Converse is false*)
+lemma "?p : (ALL x. P(x)) | (ALL x. Q(x)) --> (ALL x. P(x) | Q(x))"
+  by (tactic {* IntPr.fast_tac 1 *})
+
+lemma "?p : (ALL x. P-->Q(x))  <->  (P--> (ALL x. Q(x)))"
+  by (tactic {* IntPr.fast_tac 1 *})
+
+
+lemma "?p : (ALL x. P(x)-->Q)  <->  ((EX x. P(x)) --> Q)"
+  by (tactic {* IntPr.fast_tac 1 *})
+
+
+text "Some harder ones"
+
+lemma "?p : (EX x. P(x) | Q(x)) <-> (EX x. P(x)) | (EX x. Q(x))"
+  by (tactic {* IntPr.fast_tac 1 *})
+
+(*Converse is false*)
+lemma "?p : (EX x. P(x)&Q(x)) --> (EX x. P(x))  &  (EX x. Q(x))"
+  by (tactic {* IntPr.fast_tac 1 *})
+
+
+text "Basic test of quantifier reasoning"
+(*TRUE*)
+lemma "?p : (EX y. ALL x. Q(x,y)) -->  (ALL x. EX y. Q(x,y))"
+  by (tactic {* IntPr.fast_tac 1 *})
+
+lemma "?p : (ALL x. Q(x))  -->  (EX x. Q(x))"
+  by (tactic {* IntPr.fast_tac 1 *})
+
+
+text "The following should fail, as they are false!"
+
+lemma "?p : (ALL x. EX y. Q(x,y))  -->  (EX y. ALL x. Q(x,y))"
+  apply (tactic {* IntPr.fast_tac 1 *})?
+  oops
+
+lemma "?p : (EX x. Q(x))  -->  (ALL x. Q(x))"
+  apply (tactic {* IntPr.fast_tac 1 *})?
+  oops
+
+lemma "?p : P(?a) --> (ALL x. P(x))"
+  apply (tactic {* IntPr.fast_tac 1 *})?
+  oops
+
+lemma "?p : (P(?a) --> (ALL x. Q(x))) --> (ALL x. P(x) --> Q(x))"
+  apply (tactic {* IntPr.fast_tac 1 *})?
+  oops
+
+
+text "Back to things that are provable..."
+
+lemma "?p : (ALL x. P(x)-->Q(x)) & (EX x. P(x)) --> (EX x. Q(x))"
+  by (tactic {* IntPr.fast_tac 1 *})
+
+
+(*An example of why exI should be delayed as long as possible*)
+lemma "?p : (P --> (EX x. Q(x))) & P --> (EX x. Q(x))"
+  by (tactic {* IntPr.fast_tac 1 *})
+
+lemma "?p : (ALL x. P(x)-->Q(f(x))) & (ALL x. Q(x)-->R(g(x))) & P(d) --> R(?a)"
+  by (tactic {* IntPr.fast_tac 1 *})
+
+lemma "?p : (ALL x. Q(x))  -->  (EX x. Q(x))"
+  by (tactic {* IntPr.fast_tac 1 *})
+
+
+text "Some slow ones"
+
+(*Principia Mathematica *11.53  *)
+lemma "?p : (ALL x y. P(x) --> Q(y)) <-> ((EX x. P(x)) --> (ALL y. Q(y)))"
+  by (tactic {* IntPr.fast_tac 1 *})
+
+(*Principia Mathematica *11.55  *)
+lemma "?p : (EX x y. P(x) & Q(x,y)) <-> (EX x. P(x) & (EX y. Q(x,y)))"
+  by (tactic {* IntPr.fast_tac 1 *})
+
+(*Principia Mathematica *11.61  *)
+lemma "?p : (EX y. ALL x. P(x) --> Q(x,y)) --> (ALL x. P(x) --> (EX y. Q(x,y)))"
+  by (tactic {* IntPr.fast_tac 1 *})
+
+end```