  Session type systems have been given logical foundations via Curry-Howard
correspondences based on both intuitionistic and classical linear logic. The
type systems derived from the two logics enforce communication correctness on
the same class of pi-calculus processes, but they are significantly different.
Caires, Pfenning and Toninho informally observed that, unlike the classical
type system, the intuitionistic type system enforces locality for shared
channels, i.e. received channels cannot be used for replicated input. In this
paper, we revisit this observation from a formal standpoint. We develop United
Linear Logic (ULL), a logic encompassing both classical and intuitionistic
linear logic. Then, following the Curry-Howard correspondences for session
types, we define piULL, a session type system for the pi-calculus based on ULL.
Using piULL we can formally assess the difference between the intuitionistic
and classical type systems, and justify the role of locality and symmetry
therein.
