The Frobenius Problem in a Free Monoid. - Jui-Yi Kao; Jeffrey O. Shallit; Zhi Xu 002 (STACS, 2008)

An NP-hardness Result on the Monoid Frobenius Problem - Zhi Xu 002; Jeffrey O. Shallit (CoRR, 2008)

Decision problems for convex languages. - Janusz A. Brzozowski; Jeffrey O. Shallit; Zhi Xu 002 (Inf. Comput., 2011)

The Computational Complexity of Universality Problems for Prefixes, Suffixes, Factors, and Subwords of Regular Languages. - Narad Rampersad; Jeffrey O. Shallit; Zhi Xu 002 (Fundam. Informaticae, 2012)