  Protocols provide the unifying glue in concurrent and distributed software
today; verifying that message-passing programs conform to such governing
protocols is important but difficult. Static approaches based on multiparty
session types (MPST) use protocols as types to avoid protocol violations and
deadlocks in programs. An elusive problem for MPST is to ensure both protocol
conformance and deadlock freedom for implementations with interleaved and
delegated protocols. We address this relevant problem by proposing a
decentralized analysis of multiparty session protocols for asynchronous
processes with recursion. Our solution rests upon APCP, a new type system that
ensures protocol conformance and deadlock freedom with respect to binary
protocols. Our analysis enables the sound and complete transfer of correctness
from APCP to multiparty session protocols.
