Tree-systems of morphisms

Abstract. Starting from the idea of determinism in membrane systems, we introduce a language generating device consisting of morphisms placed in the nodes of a tree. Initial strings are given in the leaves; by iteratively applying the morphisms to them, we produce new strings, which are collected in the root of the tree. Such a device is called a tree-system of morphisms (in short, a T system). We investigate here the power of T systems, both in the extended (a terminal alphabet is considered and only strings over it are accepted) and non-extended case, mainly in comparison with classes of languages in Lindenmayer hierarchy.