1. Brown, D. R. and R. S. Houston,Cancellative semigroups on manifolds, Semigroup Forum35 (1987) 279–302.
2. Carruth, J. H., J. A. Hildebrant, and R. J. Koch “The Theory of Topological Semigroups, I and II,” Marcel Dekker, New York, 1983 and 1986.
3. Comfort, W. W., K. H. Hofmann, and D. Remus, “Topological groups and semigroups,” in: M. Hušek and J. van Mill, Eds., Recent Progress in General Topology, Elsevier, 1992, 57–144.
4. Dieudonné, J.,Orientation générale des mathématiques pures and 1973, Gazette des Mathématiciens1 (1974), 73–97.
5. de Leeuw, K. and I. Glicksberg,1. Applications of almost periodic compactifications. 2. Almost periodic functions on semigroups, Acta Math.105 (1961), 63–98, and 99–140.