  In the setting of the pi-calculus with binary sessions, we aim at relaxing
the notion of duality of session types by the concept of retractable compliance
developed in contract theory. This leads to extending session types with a new
type operator of "speculative selection" including choices not necessarily
offered by a compliant partner. We address the problem of selecting successful
communicating branches by means of an operational semantics based on
orchestrators, which has been shown to be equivalent to the retractable
semantics of contracts, but clearly more feasible. A type system, sound with
respect to such a semantics, is hence provided.
