Abstract
We establish a correspondence between (fragments of) TELO, a temporal extension of the EL description logic with the LTL operator Ok, and some specific kinds of formal grammars, in particular, conjunctive grammars (context-free grammars equipped with the operation of intersection). This connection implies that TELO does not possess the property of ultimate periodicity of models, and further leads to undecidability of query answering in TELO, closing a question left open since the introduction of TELO. Moreover, it also allows to establish decidability of query answering for some new interesting fragments of TELO, and to reuse for this purpose existing tools and algorithms for conjunctive grammars.