The class of all semigroups related to semihypergroups of order 2
Somnuek Worawiset, Jörg Koppitz, Somchit Chotchaisthit · Mathematica Slovaca · 2019
Abstract This paper deals with semihypergroups of order two from the point of view of the model theory. We use basic knowledge to show that there are exactly 17 non-isomorphic semihypergroups of order two. Each of them corresponds in a canonical way to a semigroup of order three. We classify all of them by generalized identities a concept introduced by Lyapin. In particular, we classify all non-group semigroups of order three by one generalized identity.