Wilfried Buchholz

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It is one of Kurt Schiitte's great merits to have established cut-elimination on infinitary derivations as a powerful and elegant tool for proof-theoretic investigations. Compared to the Gentzen-Takeuti approach where ordinals are assigned to finite derivations in a rather cryptic way, the use of infinitary derivations together with the canonical assignment(More)
Introduction 131 In Kirby and Paris [5] it was shown that a certain combinatorial statement (conceming finite trees) is independent of Peano Arithmetic. Here we present a not too complicated extension of tbis statement and prove its independence from the riluch stronger theory (II~-CA) + BI. This is done by refining the methods which we have developed in(More)