Strong normalization for second order classical natural deduction

Abstract

The strong normalization theorem for second-order classical natural deduction is proved. The method used is an adaptation of the one of reducibility candidates introduced in a thesis by J.Y. Girard (Univ. Paris 7, 1972) for second-order intuitionistic natural deduction. The extension to the classical case requires, in particular, a simplification of the notion of reducibility candidates.<>