  We deal with a normal form for context-free grammars, called Dyck normal
form. This normal form is a syntactical restriction of the Chomsky normal form,
in which the two nonterminals occurring on the right-hand side of a rule are
paired nonterminals. This pairwise property, along with several other terminal
rewriting conditions, makes it possible to define a homomorphism from Dyck
words to words generated by a grammar in Dyck normal form. We prove that for
each context-free language L, there exist an integer K and a homomorphism phi
such that L=phi(D'_K), where D'_K is a subset of D_K and D_K is the one-sided
Dyck language over K letters. As an application we give an alternative proof of
the inclusion of the class of even linear languages in AC1.
