1. Math. Surveys;A.H. Clifford,1961
2. Drbohlav, K.,A note on epimorphisms in algebriac categories, Comment. Math. Univ. Carolinae 4, 2 (1963).
3. Hall, T.E. and P.R. Jones,Epis are onto for finite regular semigroups, Proc. Edinburgh Math. Soc., to appear.
4. Higgins, P.M.,The commutative varieties of semigroups for which epis are onto, Proc. Edinburgh Math. Soc., to appear.
5. Higgins, P.M.,Saturated and epimorphically closed varieties of semigroups, J. Austral. Math. Soc., to appear.