Main=<s>String.
A : B | E common.
B=<x> X <X> X <a> X <y> D <z> B D.
C : G.
E=D F D<a>X.
G=<a> A <b> B <y> D <z> B D.
X=.


// the only complain should be in E
// it should recognize the difference between capital<X> and small <x>