N. Kehayopulu and M. Tsingelis
Fuzzy ideals in ordered semigroups
The right (left) ideals, quasi- and bi-ideals
play an essential role in studying the structure of some ordered
semigroups. In an attempt to show how similar is the theory of
ordered semigroups based on ideals or ideal elements with the
theory of ordered semigroups based on fuzzy ideals, keeping the
usual definitions of fuzzy right ideal, fuzzy left ideal, fuzzy
quasi-ideal and fuzzy bi-ideal, we show here that in ordered
groupoids, the fuzzy right (resp. left) ideals are fuzzy
quasi-ideals and in ordered semigroups, the fuzzy quasi-ideals are
fuzzy bi-ideals. Moreover, we prove that in regular ordered
semigroups, the fuzzy quasi-ideals and the fuzzy bi-ideals
coincide. We finally show that in an ordered semigroup the fuzzy
quasi-ideals are just intersections of fuzzy right and fuzzy left
ideals.