A natural bijection for contiguous pattern avoidance in words
Abstract
Two words p and q are avoided by the same number of length-n words, for all n, precisely when p and q have the same set of border lengths. Previous proofs of this theorem use generating functions but do not provide an explicit bijection. We give a bijective proof for all pairs p, q that have the same set of proper borders, establishing a natural bijection from the set of words avoiding p to the set of words avoiding q.
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