Bing Jun YU
In this paper a natural relationship between categories and semigroups established by the biorder of idempotents in semigroups is investigated. For every semigroup S with idempotents, via the biorder ωl,ωr, the sets of left and right principal ideals generated by idempotents naturally determine two categories L(S),R(S) with subobjects and images in which every inclusion is right split. The properties of morphisms in these two categories naturally correspond to the abundance or regularity of elements in S. By applying this relationship, the concepts of “balanced, abundant or normal categories” are defined. For each balanced (abundant or normal) category C, the “cone semigroup” TC of C is constructed. It is proved that TC is a left abundant (abundant or regular) semigroup, a left abundant (abundant or regular) semigroup (monoid) S is isomorphic with a subsemigroup of TL(S) (with TL(S)), every balanced (abundant or normal) category C is isomorphic with the ideal category L(S) of some left abundant (abundant or regular) semigroup S, as categories with subobjects.