Characterizing Recursive Programs up to Bisimilarity

A recursive program is determined, up to bisimilarity, by the operation of the recursion body on arbitrary processes, of which it is a fixpoint. The traditional proof of this fact uses Howe’s method, but that does not tell us how the fixpoint is obtained. In this paper, we show that the fixpoint may be obtained by a least fixpoint procedure iterated through the hierarchy of countable ordinals, using Groote and Vaandrager’s notion of nested simulation.