## FOL: First-Order Logic with Natural Deduction

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.

The `ex` subdirectory contains some examples.

Useful references on First-Order Logic:

- Simon Thompson, Type Theory and Functional Programming (Addison-Wesley, 1991)
  (The first chapter is an excellent introduction to natural deduction in general.)
- Antony Galton, Logic for Information Technology (Wiley, 1990)
- Michael Dummett, Elements of Intuitionism (Oxford, 1977)