1. Berstel, J., Sur les pôles et le quotient de Hadamard de séries N-rationelles. C.R. Acad. Sc. Paris, t. 272, 1079–1081 (1971).
2. Berstel, J. and Mignotte, M., Deux proprietes decidables des suites recurrentes lineaires. Seminaire d'Informatique, Univ. Louis Pasteur, Strasbourg (1975).
3. Ginsburg, S. and Rovan, B., On the periodicity of word-length in D0L languages. Information and Control 26 (1974).
4. Herman, G and Rozenberg, G., Developmental Systems and Languages. North-Holland Publ. Co. (1975).
5. Karhumäki, J., Two theorems concerning recognizable N-subsets of σ *. Theoretical Computer Science, to appear.