(University of Leeds)

In many a proof by contradiction of a universal statement the existence of a minimal counterexample is proved by the Lemma of Kuratowski-Zorn.Whenever minimal logic suffices for establishing the hypotheses, one can reread the proof as a direct and inductive proof with the principle of Open Induction by Jean-Claude Raoult.

(This work was prompted by a communication by Ulrich Berger.)

Robert Recorde Room

Department of Computer Science