  Although regular expressions do not correspond univocally to regular
languages, it is still worthwhile to study their properties and algorithms. For
the average case analysis one often relies on the uniform random generation
using a specific grammar for regular expressions, that can represent regular
languages with more or less redundancy. Generators that are uniform on the set
of expressions are not necessarily uniform on the set of regular languages.
Nevertheless, it is not straightforward that asymptotic estimates obtained by
considering the whole set of regular expressions are different from those
obtained using a more refined set that avoids some large class of equivalent
expressions. In this paper we study a set of expressions that avoid a given
absorbing pattern. It is shown that, although this set is significantly smaller
than the standard one, the asymptotic average estimates for the size of the
Glushkov automaton for these expressions does not differ from the standard
case.
