Allows more backtracking in proof reconstruction, making it slower but more
robust (avoiding PROOF FAILED)
Record type of branches, better tracing, etc.
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<H2>FOL: First-Order Logic with Natural Deduction</H2>
This directory contains the ML sources of the Isabelle system for
First-Order Logic (constructive and classical versions). For a
classical sequent calculus, see LK.<p>
The <tt>ex</tt> subdirectory contains some examples.<p>
Useful references on First-Order Logic:
<UL>
<LI> Simon Thompson, Type Theory and Functional Programming (Addison-Wesley, 1991)<br>
(The first chapter is an excellent introduction to natural
deduction in general.)
<LI>Antony Galton, Logic for Information Technology (Wiley, 1990)
<LI>Michael Dummett, Elements of Intuitionism (Oxford, 1977)
</UL>
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