Pattern Avoidability with Involution

An infinte word w avoids a pattern p with the involution θ if there is no substitution for the variables in p and no involution θ such that the resulting word is a factor of w. We investigate the avoidance of patterns with respect to the size of the alphabet. For example, it is shown that the pattern α θ (α)α can be avoided over three letters but not two letters, whereas it is well known that α α α is avoidable over two letters.