We saw in the previous post that π -calculus is a process calculus which is dependent on a theory of names; it is therefore said that it is not a closed theory. The ρ -calculus is an asynchronous message-passing calculus built on a notion of quoting; it is a closed theory, as the theory of names is wholly determined by the theory of processes. The name ρ -calculus or RHO-calculus is an acronym for reflective, higher-order calculus . By reflective, we mean there is a mechanism for switching between names and processes (quote/dereference, see below). By higher-order, we mean that the resulting language is very expressive.