Note on a Double Coset Decomposition of Semigroups due to Štefan Schwarz Alfred Hoblitzelle Clifford — 1963 Matematicko-fyzikálny časopis
The first sixty-five years - Clifford Alfred D.D. Miller; ALFRED HOBLITZELLE CLIFFORD — 1974 Semigroup forum
Union and symmetry preserving endomorphisms of the semigroup of all binary relations on a set Alfred Hoblitzelle Clifford; D. D. Miller — 1970 Czechoslovak Mathematical Journal