"In a process-algebraic approach to system verification, one typically writes two specifications. One, call it SYS, captures the design of the actual system and the other, call it SPEC, describes the system's desired 'high-level' behavior. One may then establish the correctness of SYS with respect to SPEC by showing that SYS behaves the 'same as' SPEC." ( The approach described is used for the calculus of communicating systems (CCS), an important actor in process calculus, a branch of Computer Science that formally models concurrent systems. However, this approach was not adopted when the reversible calculus of communicating systems (RCCS) was defined. Our current investigation aims at understanding if there is a fundamental reason not to do so, and this lead us to also question how a syntactic equivalence used to go from SYS CCS to SPEC CCS was defined.