Cross-sections for finitely presented monoids with decidable word problems
Rewriting Techniques and Applications, Lecture Notes in Computer Science 1997
New Pumping lemma for context-free languages
Combinatorics, Complexity, and Logic, Lecture Notes in Computer Science 1996
On shuffle closures of commutative regular languages
Combinatorics, Complexity, and Logic, Lecture Notes in Computer Science 1996
On transitive cofinal automata
Mathematical Aspects of Natural and Formal Languages (edited by Gh. Paun), World Scientific, 1995
Decomposition of total commutations
Words, Languages and Combinatorics II, World Scientific 1994