Constructive Mathematics - Maintained by Fred Richards. www.math.fau.edu/Richman/html/construc.htm
Intuitionistic Logic - A short entry in the Stanford Encyclopaedia of Philosophy by Joan R. Moschovakis. plato.stanford.edu/entries/logic-intuitionistic
Porgi - Porgi is a Proof-Or-Refutation Generator for Intuitionistic propositional logic, implementated by Allen Stoughton. Given a sequent, Porgi either finds a minimally sized, normal natural deduction of the sequent, or it finds a "small", tree-based Kripke countermodel of the sequent. It is written in Standard ML. www.cis.ksu.edu/~allen/porgi.html
