Original Article

Acta Informatica

, Volume 48, Issue 1, pp 1-18

Some properties of the disjunctive languages contained in Q

  • Zheng-Zhu LiAffiliated withCenter of General Education, Aletheia University on Motou Campus Email author 
  • , Y. S. TsaiAffiliated withDepartment of Applied Mathematics, Chung-Yuan Christian University

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The set of all primitive words Q over an alphabet X was first defined and studied by Shyr and Thierrin (Proceedings of the 1977 Inter. FCT-Conference, Poznan, Poland, Lecture Notes in Computer Science 56. pp. 171–176 (1977)). It showed that for the case |X| ≥ 2, the set along with \({Q^{(i)} = \{f^i\,|\,f \in Q\}, i\geq 2}\) are all disjunctive. Since then these disjunctive sets are often be quoted. Following Shyr and Thierrin showed that the half sets \({Q_{ev} = \{f \in Q\,|\,|f| = {\rm even}\}}\) and Q od = Q \ Q ev of Q are disjunctive, Chien proved that each of the set \({Q_{p,r}= \{u\in Q\,|\,|u|\equiv r\,(mod\,p) \},\,0\leq r < p}\) is disjunctive, where p is a prime number. In this paper, we generalize this property to that all the languages \({Q_{n,r}= \{u\in Q\,|\,|u|\equiv r\,(mod\,n) \},\, 0\leq r < n}\) are disjunctive languages, where n is any positive integer. We proved that for any n ≥ 1, k ≥ 2, (Q n,0) k are all regular languages. Some algebraic properties related to the family of languages {Q n,r | n ≥ 2, 0 ≤ r < n } are investigated.