A note on pseudocongruences in semigroups. Kehayopulu, N.; Tsingelis, M. — 2002 Lobachevskii Journal of Mathematics
Bi-ideals in ordered semigroups and ordered groups. Kehayopulu, N.; Ponizovskij, J.S.; Tsingelis, M. — 1999 Zapiski Nauchnykh Seminarov POMI
The embedding of an ordered semigroup in a simple one with identity. N. Kehayopulu; M. Tsingelis — 1996 Semigroup forum
On the decomposition of prime ideals of ordered semigroups into their N-classes. N. Kehayopulu; M. Tsingelis — 1993 Semigroup forum