Computations in Coordinated Pair Systems

Selective substitution grammars provide a rather general framework for the grammatically oriented formal language theory (see, e.g., [R1], [K], and [KR]). They were generalized in [R2] to coordinated table selective substitution systems (ds systems) which provide a convenient unifying framework for both grammars and machines (automata). The present paper investigates coordinated pair (cp) systems which form a subclass of cts systems corresponding in a very natural way to push-down automata: thus cp systems generate context-free languages (all and only). This paper investigates the structure of computations in cp systems.