A : B1 | C *common* <z> Z.
B1 : B2.
B2 : B.
B = <z> X.
C = X X.
G = "g".
X = "x".
Y = <g> G <g> Z. 
Z = "z".

// This is a test for unique parts
// Notice that class B has two parts named "z"
// Also, Class Y has two "g" parts
// C has two X parts.