  In this paper we introduce imprecise probability for session types. More
exactly, we use a probabilistic process calculus in which both nondeterministic
external choice and probabilistic internal choice are considered. We propose
the probabilistic multiparty session types able to codify the structure of the
communications by using some imprecise probabilities given in terms of lower
and upper probabilities. We prove that this new probabilistic typing system is
sound, as well as several other results dealing with both classical and
probabilistic properties. The approach is illustrated by a simple example
inspired by survey polls.
