An iteration theorem for simple precedence languages
We have obtained powerful and reasonably general tools for proving that languages are not simple precedence when that is the case. We have also been able to give a systematic way of producing simple precedence grammars in certain situations.
An extension of the precedence relations between two symbols is obtained by defining precedence relations between strings of length m and n (cf [AU1]). Thus the family of uniquely invertible (m,n) precedence languages is obtained. Our iteration theorem may be generalized to deal with uniquely invertible (1,k) precedence languages, and using it we determine that all the languages proved in the literature to be non-SPL are not uniquely invertible (1,k) precedence for any k ⩾ 1. This is particularly interesting since it is not known if the families of uniquely invertible (1,k) precedence languages form a hierarchy [AU2,S]. (Note that uniquely invertible (2,1) precedence languages coincide with the deterministic languages [G].) Details of this generalization, as well as additional comments, may be found in the full text [KY].
KeywordsPrecedence Relation Counting Scheme Sentential Form Typical Derivation Nonterminal Symbol
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