On purely morphic characterizations of context-free languages

AbstractIn this paper we show the following: For any λ-free context-free language L there effectively exist a weak coding g, a homomorphism h such that L=gh−1 (∣cD2), where D2 is the Dyck set over a two-letter alphabet. As an immediate corollary it follows that for any λ-free context-free language L there exist a weak coding g and a mapping F such that L=gF−1(∣c)

Algebraic Systems and Pushdown Automata

The theory of algebraic power series in noncommuting variables, as we un-derstand it today, was initiated in [2] and developed in its early stages by the French school. The main motivation was the interconnection with context-free grammars: the defining equations were made to correspond to context-fre

New Results on Context-Free Tree Languages

Context-free tree languages play an important role in algebraic semantics and are applied in mathematical linguistics. In this thesis, we present some new results on context-free tree languages