Productions are one of the following two forms / A → σx where σ ∈ T and x ∈ V* (Front terminal only)
Claim
Given a CFG G, we can compute an equivalent CFG G' in GNF. This implies that, for every CFL L, there exists a CFG in GNF for L
Proof
eliminate the followings needed
(a) Front recursions: A → AB
(b) Front non-terminals: A → BCa
(c) Non-front terminals: A → bBaC