A code implements an algorithm. Following Irmak [8], we take here an algorithm to mean a pattern of instructions, i.e. an abstract entity, a sort of process universal that is then correlated to a class of possible process executions. So, two different codes c1 and c2 can be semantically equivalent (e.g., by being able to generate the same class of possible process executions) if they implement the same algorithm, while being differ- ent codes. For instance, if c2 is produced from c1 by variable renaming, inclusion of comments and modularization, c2 can possess a number of properties (e.g., in terms of understandability, maintainability, aesthetics) that are lacking in c1.