Un sous-ensemble intéressant du français
Unavoidable set : extension and reduction
Unavoidable Set: Extension and Reduction
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.