  Session types are types for specifying the protocols that communicating
processes must follow in a concurrent system. When composing two or more
well-typed processes, a session typing system must check whether such processes
are multiparty compatible, a property that guarantees that all sent messages
are eventually received and no deadlock ever occurs. Previous work has shown
that duality and the more general notion of coherence are sufficient syntactic
conditions for guaranteeing the multiparty compatibility property. In this
paper, following a propositions-as-types fashion which relates session types to
linear logic, we generalise coherence to forwarders. Forwarders are processes
that act as middleware by forwarding messages according to a given protocol.
Our main result shows that forwarders not only generalise coherence, but fully
capture all well-typed multiparty compatible processes.
