Constrained Multi-Tildes: Derived Term and Position Automata

Abstract: Multi-tildes are regular operators that were introduced to enhance the factorization power of regular expressions, allowing us to add the empty word in several factors of a catenation product of languages. In addition to multi-bars, which dually remove the empty word, they allow representing any acyclic automaton by a linear-sized expression, whereas the lower bound is exponential in the classic case. In this paper, we extend multi-tildes from disjunctive combinations to any Boolean combination, allowing us to exponentially enhance the factorization power of tildes expressions. Moreover, we show how to convert these expressions into finite automata and give a Haskell implementation of them using advanced techniques of functional programming.