  Based on an analysis of the inference rules used, we provide a
characterization of the situations in which classical provability entails
intuitionistic provability. We then examine the relationship of these
derivability notions to uniform provability, a restriction of intuitionistic
provability that embodies a special form of goal-directedness. We determine,
first, the circumstances in which the former relations imply the latter. Using
this result, we identify the richest versions of the so-called abstract logic
programming languages in classical and intuitionistic logic. We then study the
reduction of classical and, derivatively, intuitionistic provability to uniform
provability via the addition to the assumption set of the negation of the
formula to be proved. Our focus here is on understanding the situations in
which this reduction is achieved. However, our discussions indicate the
structure of a proof procedure based on the reduction, a matter also considered
explicitly elsewhere.
