1. H.Ahrends, Endomorphismenmonoide von Graphen und Distributivgesetze f�r Kompositionen von Graphen. Diplomarbeit, Oldenburg 1987.
2. K. ?ulik, Zur Theorie der Graphen. Casopis Pest. Mat.83, 133?155 (1958).
3. V. Fleischer, On the wreath product of monoids with categories. Proc. Acad. Sci. Estonian SSR35, 237?243 (1986) (in Russian).
4. V. Fleischer andU. Knauer, Endomorphism monoids of acts are wreath products of monoids with small categories. In: LNM1320, 84?96, Berlin-Heidelberg-New York 1988.
5. F.Harary, Graph theory. Reading, Mass. 1969.