A a direct proof of Ramsey's theorem
Found around 1994. This proof looks like a cut-elimination.
A constructive topological proof of van der Waerden's theorem.
A Note on the Open Induction Principle
A proof of Higman's lemma by structural induction
Towards an intuitionistic fixpoint theorem (1987)
Last modified: Tue Aug 17 10:44:57 MET DST 1999