  We introduce the notion of finitary computable reducibility on equivalence
relations on the natural numbers. This is a weakening of the usual notion of
computable reducibility, and we show it to be distinct in several ways. In
particular, whereas no equivalence relation can be $\Pi_{n+2}$-complete under
computable reducibility, we show that, for every $n$, there does exist a
natural equivalence relation which is $\Pi_{n+2}$-complete under finitary
reducibility. We also show that our hierarchy of finitary reducibilities does
not collapse, and illustrate how it sharpens certain known results. Along the
way, we present several new results which use computable reducibility to
establish the complexity of various naturally defined equivalence relations in
the arithmetical hierarchy.

Logic