Idempotents and product representations with applications to the semigroup of binary relations. G. Markowsky — 1972 Semigroup forum
The Schützenberger group of an H-class in the semigroup of binary relations. D.W. Hardy; G. Markowsky; R.L. Brandon — 1972 Semigroup forum
Cardinalities of D-classes in Bn. K.K.H. Butler; R. Brandon; D.W. Hardy; G. Markowsky — 1972 Semigroup forum