Unavoidable Set: Extension and Reduction
Department of Applied Mathematics,
Hanoi Institute of Technology,
1 Dai Co Viet, Hanoi, Vietnam.
2 Hanoi Institute of Mathematics, P.O. Box 631, Bo Ho, 10 000 Hanoi, Vietnam; email@example.com.
Accepted: 15 July 1999
We give an explicit criterion for unavoidability of word sets. We characterize extendible, finitely and infinitely as well, elements in them. We furnish a reasonable upper bound and an exponential lower bound on the maximum leghth of words in a reduced unavoidable set of a given cardinality.
Mathematics Subject Classification: 68R15 / 68S05
Key words: Unavoidable set / reduced unavoidable set / extension / reduction.
© EDP Sciences, 1999