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The Theory of Topological Semigroups I. Pure and Applied Mathematics series, Marcel Dekker, Inc., New York, 1983. 
MR 0691307 
[2] Clifford, A.H., and Preston, G.B.: 
The Algebraic Theory of Semigroups I. Math. Surveys, 7, Amer. Math. Soc., 1961. 
MR 0132791