On the Complexity of Properties of Partial Bijection Semigroups

Abstract: We examine the computational complexity of problems in which we are given generators for a partial bijection semigroup and asked to check properties of the generated semigroup. We prove that the following problems are in AC$^0$: (1) enumerating left and right identities and (2) checking if the semigroup is completely regular. We prove that checking membership of a given idempotent is a PSPACE-complete problem. We also describe a nondeterministic logspace algorithm for checking if an inverse semigroup given by generators satisfies a given semigroup identity that may involve a unary inverse operation.