Verifying temporal properties using explicit approximants: completeness for context-free processes

We present a sequent calculus for formally verifying modal -calculus properties of concurrent processes. Building on work by Dam and Gurov, the proof system contains rules for the explicit manipulation of fixed-point approximants. We develop a new syntax for approximants, incorporating, in particular, a mechanism for approximant modification. We make essential use of this feature to prove our main result: the sequent calculus is complete for establishing arbitrary -calculus properties of context-free processes