1. Dassow, J.: Contextual grammars with subregular choice. Fundamenta Informaticae 64 (1-4), 109–118 (2005)
2. Istrail, S.: Gramatici contextuale cu selectiva regulata. Stud. Cerc. Mat. 30, 287–294 (1978)
3. Marcus, S.: Contextual grammars. Revue Roum. Math. Pures Appl. 14, 1525–1534 (1969)
4. Păun, G.: Marcus Contextual Grammars. Kluwer Publ. House, Dordrecht (1998)
5. Rozenberg, G., Salomaa, A. (eds.): Handbook of Formal Languages. Springer, Berlin (1997)