A = <b> B .
B = C D.
C = <a> A <i> I.
D = X.
D = "d" X.
F = List(Z).
I = Ident.
List(S) ~ {S}. 

//
// Notice that 	D is defined twice, 
//		X is undefined twice (but only one error message appears),
//		when there should be 2 messages, 
//		and Z is undefined in the parameter class
//