; It is known that the language the language L = {a^nb^nc^n | n >= 1} is not context free.
; However, with the use of the look ahead operators we can construct a grammar
; that accepts those phrases and only those phrases.
S = &(AB !b) *a BC !c
AB = a [AB] b
BC = b [BC] c
a = %s"a"
b = %s"b"
c = %s"c"