Table of Contents

and preliminaries.- A review of Gentzen's second consistency proof.- The intuitionistic system of number theory.- A formally intuitionistic system as strong as classical analysis.- Transfinite induction with respect to recursive wellorderings without function parameters.- A formally intuitonistic theory equivalent to classical transfinite induction with respect to recursive wellfounded trees with function parameters.- A system containing barinduction with respect to decidable predicates.- Harrop formulas.- The Markov principle.- Relative consistency proof of ZTN with respect to ZTi/IN*.