1. Idempotent-separating extensions of inverse semigroups;D'Alarcao;J. Austral. Math. Soc.,1969
2. A class of d-simple semigroups;Clifford;Amer. J. Math.,1953
3. The Algebraic Theory of Semigroups;Clifford,1961
4. The Algebraic Theory of Semigroups;Clifford,1967
5. The maximum idempotent-separating congruence on an inverse semigroup;Howie,1964