1.1. The emergence of materially elaborated variants of generative description of languages has brought about a pragmatical question as to whether a particular generative grammar is working in such a way as it is assumed to be. This problem proved to be unsolvable by a linguist not aided by computer. Therefore, programmes started to be written, so as to enable the computers either a) to make a grammar work or b) to allow to find out through a recognition procedure, e.g. changing the directions of arrows in all the rewriting rules whether an initial S can really be reached when starting from assumed output strings.