Main Page | See live article | Alphabetical index A context-free grammar is in Greibach normal form (GNF) iff all production rules are of the form: A -> αX where A is a nonterminal symbol, α is a terminal symbol and X is (possibly empty) sequence of nonterminal symbols. No grammar in GNF can generate the null string. Conversely, every context-free grammar which does not generate the null string can be transformed into an equivalent grammar in Greibach normal form. This can be used to prove that every context-free language can be accepted by a non-deterministic pushdown automaton. Greibach normal form is named for Sheila Greibach (1939-), who is currently Professor of Computer Science at the University of California, Los Angeles. This article is from Wikipedia. All text is available under the terms of the GNU Free Documentation License.