On Finite Bases for Weak Semantics: Failures versus Impossible Futures
  We provide a finite basis for the (in)equational theory of the process algebra BCCS modulo the weak failures preorder and equivalence. We also give positive and negative results regarding the axiomatizability of BCCS modulo weak impossible futures semantics. 
Taolue Chen, Wan Fokkink, Rob van Glabbeek