  We describe the use of quantum process calculus to describe and analyze
quantum communication protocols, following the successful field of formal
methods from classical computer science. The key idea is to define two systems,
one modelling a protocol and one expressing a specification, and prove that
they are behaviourally equivalent. We summarize the necessary theory in the
process calculus CQP, including the crucial result that equivalence is a
congruence, meaning that it is preserved by embedding in any context. We
illustrate the approach by analyzing two versions of a quantum error correction
system.
