Sets of Grammars between Context-Free and Context-Sensitive

We discuss some sets of g r a m m a r s whose generat ive power l ies between that of the set of contextf ree g r a m m a r s and that of the set of contextsensit ive g r a m m a r s . These sets a re developed by subjecting genera to rs of context-sensi t ive g r a m m a r s to abs t rac t vers ions of a "hardware" res t r i c t ion to which the u s e r s of natural languages, unlike the d e s c r i b e r s of natural languages, might be subject.