No abstract

No abstract

No abstract

No abstract

A morphism is Sturmiau if the image of every Sturmian word is a Sturmian word. Sturmian morphisms appear in number theory in connection with the so-called substitutions of characteristic sequences. A recent account of results in this direction is given by T. C. Brown in [4]. In this paper, we show that in order to test whether a morphism f is Sturmian, it suffices to check whether the single word f(ba2ba2baba2bab) is balanced. This is in fact a strengthening of a result by Mignosi, Sddbold [14]. The decidability is an immediate consequence. We also get a simpler proof of a theorem by Crisp et al. [5] characterizing those irrational numbers for which the characteristic sequence is a fixed point of a (Sturmian) morphism.* Partially supported by the PRC "Math~matiques et Informatique'.