On Descriptional Complexity of Partially Parallel Grammars

This paper presents some new results concerning the descriptional complexity of partially parallel grammars. Specifically, it proves that every recursively enumerable language is generated (i) by a four-nonterminal scattered context grammar with no more than four non-context-free productions, (ii) by a two-nonterminal multisequential grammar with no more than two selectors, or (iii) by a three-nonterminal multicontinuous grammar with no more than two selectors.