  We investigate how different fairness assumptions affect results concerning
lock-freedom, a typical liveness property targeted by session type systems. We
fix a minimal session calculus and systematically take into account all known
fairness assumptions, thereby identifying precisely three interesting and
semantically distinct notions of lock-freedom, all of which having a sound
session type system. We then show that, by using a general merge operator in an
otherwise standard approach to global session types, we obtain a session type
system complete for the strongest amongst those notions of lock-freedom, which
assumes only justness of execution paths, a minimal fairness assumption for
concurrent systems.
