Greibach normal form

A context-free grammarin Greibach normal form (GNF) iff all production rulesofform:

A -> αX

where A isnonterminal symbol, α isterminal symbolX(possibly empty) sequencenonterminal symbols.

No grammarGNF can generatenull string. Conversely, every context-free grammar which does not generatenull string can be transformed into an equivalent grammarGreibach normal form. This can be usedprove that every context-free language can be accepted bynon-deterministic pushdown automaton.

Greibach normal formnamedSheila Greibach (1939-), whocurrently ProfessorComputer Science atUniversityCalifornia, Los Angeles.