The Set of Better Quasi Orderings is Pi21-complete

In this paper we give a proof of the II$completeness of the set of countable better quasi orderings (viewed as a subset of the Cantor space). This result was conjectured by CIote in [2] and proved by the author in his Ph.d. thesis [6] (see also [7]). Here we prove it using Simpson’s definition of better quasi ordering ([15]) and as little bqo theory as… CONTINUE READING