Pathwise-randomness and models of second-order arithmetic

Abstract

A tree is pathwise-random if all of its paths are Martin-Löf random. We show that: (a) no weakly 2-random real computes a perfect pathwise-random tree; it follows that the class of perfect pathwise-random trees is null, with respect to any computable measure; (b) there exists a positive-measure pathwise-random tree which does not compute any complete extension of Peano arithmetic; and (c) there exists a perfect pathwise-random tree which does not compute any tree of positive measure and finite randomness deficiency. We then obtain models of second-order arithmetic that separate principles below weak Königs lemma.