diff -r 000000000000 -r a5a9c433f639 src/Modal/ex/S4thms.ML
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/Modal/ex/S4thms.ML	Thu Sep 16 12:20:38 1993 +0200
@@ -0,0 +1,40 @@
+(*  Title: 	91/Modal/ex/S4thms
+    ID:         $Id$
+    Author: 	Martin Coen
+    Copyright   1991  University of Cambridge
+*)
+
+(* Theorems of system S4 from Hughes and Cresswell, p.46 *)
+
+try "|- []A --> A";             (* refexivity *)
+try "|- []A --> [][]A";         (* transitivity *)
+try "|- []A --> <>A";           (* seriality *)
+try "|- <>[](<>A --> []<>A)";
+try "|- <>[](<>[]A --> []A)";
+try "|- []P <-> [][]P";
+try "|- <>P <-> <><>P";
+try "|- <>[]<>P --> <>P";
+try "|- []<>P <-> []<>[]<>P";
+try "|- <>[]P <-> <>[]<>[]P";
+
+(* Theorems for system S4 from Hughes and Cresswell, p.60 *)
+
+try "|- []P | []Q <-> []([]P | []Q)";
+try "|- ((P>-<Q) --< R) --> ((P>-<Q) --< []R)";
+
+(* These are from Hailpern, LNCS 129 *)
+
+try "|- [](P & Q) <-> []P & []Q";
+try "|- <>(P | Q) <-> <>P | <>Q";
+try "|- <>(P --> Q) <-> ([]P --> <>Q)";
+
+try "|- [](P --> Q) --> (<>P --> <>Q)";
+try "|- []P --> []<>P";
+try "|- <>[]P --> <>P";
+
+try "|- []P | []Q --> [](P | Q)";
+try "|- <>(P & Q) --> <>P & <>Q";
+try "|- [](P | Q) --> []P | <>Q";
+try "|- <>P & []Q --> <>(P & Q)";
+try "|- [](P | Q) --> <>P | []Q";
+