--- a/src/FOL/ex/int.ML Fri Jan 31 17:13:19 1997 +0100
+++ b/src/FOL/ex/int.ML Fri Jan 31 17:15:55 1997 +0100
@@ -260,7 +260,7 @@
writeln"Problem 21";
goal IFOL.thy "(EX x. P-->Q(x)) & (EX x. Q(x)-->P) --> ~~(EX x. P<->Q(x))";
-(*NOT PROVED*)
+(*NOT PROVED; needs quantifier duplication*)
writeln"Problem 22";
goal IFOL.thy "(ALL x. P <-> Q(x)) --> (P <-> (ALL x. Q(x)))";
@@ -274,8 +274,12 @@
writeln"Problem 24";
goal IFOL.thy "~(EX x. S(x)&Q(x)) & (ALL x. P(x) --> Q(x)|R(x)) & \
-\ ~(EX x.P(x)) --> (EX x.Q(x)) & (ALL x. Q(x)|R(x) --> S(x)) \
-\ --> (EX x. P(x)&R(x))";
+\ (~(EX x.P(x)) --> (EX x.Q(x))) & (ALL x. Q(x)|R(x) --> S(x)) \
+\ --> ~~(EX x. P(x)&R(x))";
+(*Not clear why fast_tac, best_tac, ASTAR and ITER_DEEPEN all take forever*)
+by Int.safe_tac;
+by (etac impE 1);
+by (Int.fast_tac 1);
by (Int.fast_tac 1);
result();