1. Graphs and Digraphs;Chartland,1996
2. The Algebraic Theory of Semigroups;Clifford,1961
3. Regularity and finiteness conditions;de Luca,1997
4. Finiteness and Regularity in Semigroups and Formal Languages;de Luca,1998
5. Rudiments of Ramsey Theory;Graham,1981