Process logic with regular formulas

The paper proposes an extension RPL of the process logic PL of Harel, Kozen and Parikh (1980). The PL formula operators f and suf are replaced by the operators chop and slice, corresponding to Kleene's regular operators · and *, thus enabling formulas to express regular sets of paths. The main result is that, in expressive power, PL<RPL, the hard part being in showing that PL≤RPL. It is argued that this version of PL comes closer to the desired goal of a natural and powerful (yet decidable) logic for reasoning about the ongoing behavior of programs.