The left-hand side of a production rule is always a nonterminal in languages that possess, for 10 points, what property, whose name refers to the inability of a language's generating symbols to delete string terminals?
This property is possessed by entities such that if one splits the yield of a tree into five parts, there are more than m marked positions in the xyz component of the yield. Ogden's Lemma gives conditions for when this property holds, and is a generalization of a theorem stating that the vwx component of a five-part string will always be less than the length p if the string is part of a set that has this property. The more complex of the two pumping lemmata applies to entities with this property, which is possessed by (*) Type-2 structures. Constructs with this property cannot generate the empty string when written in Chomsky Normal Form. The theory of languages with this property underlies LL and LR parsers. The left-hand side of a production rule is always a nonterminal in languages that possess, for 10 points, what property, whose name refers to the inability of a language's generating symbols to delete string terminals?
This property is possessed by entities such that if one splits the yield of a tree into five parts, there are more than m marked positions in the xyz component of the yield.
context-free grammar [or context-free language; prompt on CFG]