1. Cao, C.H., Yang, D., Liu, Y.: Disjunctive languages related to $$p-$$ p - primitive words, 49, 437–444 (2012).
2. Dömösi, P., Horváth, S., Ito, M.: Formal languages and primitive words. Publ. Math. Debr. 42, 315–321 (1993)
3. Dömösi, P., Horváth, S., Ito, M., Kászonyi, L., Katsura, M.: Some combinatorial properties of words, and the Chomsky-hierarchy. In: Ito, M. (ed.) Words, Languages and Combinatorics II. Proceedings of the 2nd International Conference, Kyoto, Japan, August 25–28, 1992, pp. 105–123. World Scientific, Singapore (1994)
4. Dömösi, P., Horváth, S., Ito, M., Kászonyi, L., Katsura, M.: Formal languages consisting of primitive words. LNCS 710, 194–203 (1993)
5. Fan, C.M., Huang, C.C.: A note of prefix primitive words. Acta Inform. 47, 413–423 (2010)