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+<HTML><HEAD><TITLE>Modal/ReadMe</TITLE></HEAD><BODY>
+
+<H2>Modal: First-Order Modal Sequent Calculus</H2>
+
+This directory contains the Standard ML sources of the Isabelle system for
+Modal Logic.  Important files include
+
+<DL>
+<DT>ROOT.ML
+<DD>loads all source files.  Enter an ML image containing LK
+Isabelle and type: use "ROOT.ML";<P>
+
+<DT>ex
+<DD>subdirectory containing examples.  Files Tthms.ML, S4thms.ML and
+S43thms.ML contain the theorems of Modal Logics, so arranged since
+T&lt;S4&lt;S43.  To execute them, enter an ML image containing Modal
+and type: use "ex/ROOT.ML";
+</DL>
+
+Thanks to Rajeev Gore' for supplying the inference system for S43.<P>
+
+Useful references on Modal Logics:
+
+<UL>
+<LI>Melvin C Fitting,<BR>
+    Proof Methods for Modal and Intuitionistic Logics (Reidel, 1983)
+<LI>Lincoln A. Wallen,<BR>
+    Automated Deduction in Nonclassical Logics (MIT Press, 1990)
+</UL>
+</BODY></HTML>