[1] BLYTH T., GОMES G.: On the compatibility of the natural partial order on a regular semigroup. Proc. Roy. Soc. Edinburgh Sect. A 94 (1983), 79-84. MR 0700501

[2] CLIFFОRD A. H., PRESTОN G. B.: The Algebraic Theory of Semigroups. Vol. I, II. Math. Surveys Monographs 7, Amer. Math. Soc, Providence, R.I., 1961, 1967. MR 0132791

[3] FARÉS. N.: Idempotents et D-classes dans les demigroupes et les anneaux. C.R. Acad. Sci. Paris 269 (1969), 341-343. MR 0249532

[4] GREEN J. A.: On the structure of semigroups. Ann. of Math. 54 (1951), 163-172. MR 0042380 | Zbl 0043.25601

[5] HARTWIG R.: How to partially order regular elements. Math. Japon. 25 (1980), 1-13. MR 0571255 | Zbl 0442.06006

[6] HICKEY J.: On variants of a semigroup. Bull. Austral. Math. Soc. 34 (1986), 447-459. MR 0866192 | Zbl 0586.20030

[7] HIGGINS P.: Techniques of Semigroup Theory. Clarendon Press, Оxford, 1992. MR 1167445 | Zbl 0744.20046

[8] MITSCH H.: A natural partial order for semigroups. Proc. Amer. Math. Soc. 97 (1986), 384-388. MR 0840614 | Zbl 0596.06015

[9] MITSCH H.: Subdirect products of E-inversive semigroups. J. Austral. Math. Soc. Ser. A 48 (1990), 66-78. MR 1026837 | Zbl 0691.20050

[10] NAMBООRIPAD К. S.: The natural partial order on a regular semigroup. Prоc. Edinburgh Math. Soc. (2) 23 (1980), 249-260.

[11] PETRICH M.: On extensions of semigroups determined by partial homomorphisms. Indag. Math. 28 (1966), 49-51. MR 0197610 | Zbl 0136.26601

[12] PETRICH M.: Congruences on strong semilattices of regular, simple semigroups. Semigroup Fоrum 37 (1988), 167-199. MR 0938269 | Zbl 0643.20041

[13] PETRICH M.: Introduction to Semigroups. Ch. E. Merill Publishing Company. Columbus, Ohio, 1973. MR 0393206 | Zbl 0321.20037

[14] VÁGNER V. V.: Generalized groups. (Russian), Dokl. Akad. Nauk. SSSR (N.S.) 84 (1952), 1119-1122. MR 0048425