1. The algebraic theory of semigroups I;Clifford;Am. Math. Soc. Surveys,1961
2. The algebraic theory of semigroups II;Clifford;Am. Math. Soc. Surveys,1967
3. Decision problems of finite automata design and related arithmetics;Elgot;Trans. Am. Math. Soc.,1961
4. Representation of events in nerve nets and finite automata. The Rand Corporation, Rm-704 (1951), and Automata studies;Kleene;Ann. Math. Studies,1956
5. Semigroups;Ljapin,1960