Interassociativity and three-element doppelsemigroups

Abstract

In the paper we characterize all interassociates of some non-inverse semigroups and describe up to isomorphism all three-element (strong) doppelsemigroups and their automorphism groups. We prove that there exist $75$ pairwise non-isomorphic three-element doppelsemigroups among which $41$ doppelsemigroups are commutative. Non-commutative doppelsemigroups are divided into $17$ pairs of dual doppelsemigroups. Also up to isomorphism there are $65$ strong doppelsemigroups of order $3$, and all non-strong doppelsemigroups are not commutative.