Like a namesake type of language, these things were developed and formalized by Stephen Kleene, who defined concatenation, union, and his namesake star for them.
The cycle rank, or loop complexity, of a directed graph is related to a quantity for these things according to a theorem devised by Eggan. These things can be converted to an NFA by constructing partial NFAs and putting them together with an epsilon transition, as is done by Thompson's construction algorithm. Like a namesake type of language, these things were developed and formalized by Stephen Kleene, who defined concatenation, union, and his namesake star for them. A backreference in these things can be created using parentheses. The asterisk quantifier is used to match the previous group or character zero or more times in Perl's system for them. For 10 points, identify these notations used for pattern matching that describe a set of strings, so-called "expressions".
The cycle rank, or loop complexity, of a directed graph is related to a quantity for these things according to a theorem devised by Eggan.
regular expressions [or regexp; or regular sets; or rational expressions; or regular languages; accept just regular after "expressions" is read; prompt on "patterns"]