Introduction Regular expressions are one of the most ubiquitous formalisms of theoretical computer science. Commonly, they are understood in terms of their denotational semantics, that is, through formal languages — the regular languages. This view is inductive in nature: two primitives are equivalent if they are constructed in the same way. Alternatively, regular expressions can be understood in terms of their operational semantics, that is, through finite automata. This view is coindu...
