  Session types define protocols that processes must follow when communicating.
The special case of binary session types, i.e. type annotations of protocols
between two parties, is known to be in a propositions-as-types correspondence
with linear logic. In previous work, we have shown that the generalization to
multiparty session types can be expressed either by coherence proofs or by
arbiters, processes that act as middleware by forwarding messages according to
the given protocol. In this paper, following the propositions-as-types fashion,
we generalize arbiters to a logic, which we call forwarder logic, a fragment of
classical linear logic still satisfying cut-elimination. Our main result is
summarized as follows: forwarders generalize coherence and give an elegant
proof-theoretic characterization of multiparty compatibility, a property of
concurrent systems guaranteeing that all sent messages are eventually received
and no deadlock ever occurs.
