  An infinte word w avoids a pattern p with the involution t if there is no
substitution for the variables in p and no involution t 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 a t(a) a
can be avoided over three letters but not two letters, whereas it is well known
that a a a is avoidable over two letters.
