REFERENCES
- Blyth , T. S. , Janowitz , M. F. ( 1972 ) . Residuation Theory . Oxford : Pergamon .
- Bulman-Fleming , S. , McDowell , K. ( 1983 ). Absolutely flat semigroups . Pacific J. Math. 107 : 319 – 333 .
- Bulman-Fleming , S. , Gould , V. ( 2002 ). Axiomatisability of weakly flat, flat and projective . S-acts. Comm. Alg. 30 : 5575 – 5593 .
- Bulman-Fleming , S. , Kilp , M. ( 2002 ). Equalizers and flatness properties of acts . Comm. Algebra 30 : 1475 – 1498 . [CROSSREF]
- Chen , Y. , Shum , K. P. ( 1999 ). Projective and indecomposable . S-acts. Sci. China. 42 ( Ser A ): 593 – 599 .
- Fakhruddin , S. M. ( 1986 ). Absolute flatness and amalgams in pomonoids . Semigroup Forum 33 : 15 – 22 .
- Fakhruddin , S. M. ( 1988 ). On the category of S-posets . Acta Sci. Math. (Szeged) 52 : 85 – 92 .
- Kilp , M. , Knauer , U. (1987). Characterization of monoids by properties of regular acts. J. Pure Appl. Algebra 46:217–231. [CROSSREF]
- Kilp , M. , Knauer , U. , Mikhalev , A. V. ( 2000 ) . Monoids; Acts and Categories, with Applications to Wreath Products and Graphs . Berlin : Walter de Gruyter
- Knauer , U. ( 1972 ). Projectivity of acts and Morita equivalence of monoids . Semigroup Forum 3 : 359 – 370 .
- Knauer , U. , Mikhalev , A. V. ( 1985 ). Wreath products of ordered semigroups; II. Inverse ordered wreath products . Semigroup Forum 31 : 181 – 191 .
- Liu , Z. K. ( 1993 ). A characterization of regular monoids by flatness of left acts . Semigroup Forum 46 : 85 – 89 .
- Liu , Z. K. ( 1998 ) . Theory of S-acts over Semigroups . Beijing : Science Press , (in Chinese) .
- Liu , Z. K. , Yang , Y. B. ( 1994 ). Monoids over which every flat right act satisfies (P) . Comm. Algebra 22 : 2861 – 2875 .
- Qiao , H. S. ( 2002 ). Strong flatness properties of right S-acts satisfying condition (P) . Comm. Algebra 30 : 4321 – 4330 . [CROSSREF]
- Renshaw , J. ( 2000 ). Monoids for which condition (P) acts are projective . Semigroup Forum 61 : 46 – 56 .
- Skornjakov , L. A. ( 1986 ). On the injectivity of ordered left acts over monoids . Vestnik Moskov. Univ. I Mat. Math. . 3 : 17 – 19 . (in Russian)
- Talwar , S. ( 1995 ). Morita equivalence for semigroups . J. Austral. Math. Soc. 59 ( Ser A ): 81 – 111 .
- Talwar , S. ( 1996 ). Strong Morita equivalence and a generalization of the Rees theorem . J. Algebra 181 : 371 – 394 . [CROSSREF]
- Tran , L. H. ( 1985 ). Characterization of monoids by regular acts . Perod. Sci. Math. Hung. 16 : 273 – 297 .
- #Communicated by Higgins.
- ‡Dedicated to Professor Wenting Tong on the occasion of his 65th birthday.