1. The Algebraic Theory of Semigroups;Clifford,1961
2. The Algebraic Theory of Semigroups;Clifford,1967
3. The Theory of Groups;Hall,1959
4. Zig-zag representations and inverse semigroups;McAlister;J. Algebra,1974
5. Groups, semilattices and inverse semigroups;McAlister;Trans. Amer. Math. Soc.,1974