1. P. S. Aleksandrov,Combinatorial Topology, Vol. 1, Graylock, Rochester, N. Y., 1956.
2. J. Baillieul, Green's relations in finite function semigroups,Aequationes Math. 7 (1971), 22–27.
3. C. Bass andK. K.-H. Butler, Combinatorial properties of partial transformation semigroups, unpublished, 1972.
4. G. Birkhoff,Lattice Theory, Amer. Math. Soc., Providence, R. I., 1967.
5. R. L. Brandon, K. K.-H. Butler, D. W. Hardy andG. Markowsky, Cardinalities ofD-classes inB n,Semigroup Forum 4 (1972), 341–344.