// This is a tree-shaped partial ordering (no multiple inheritance)

B, C, D <| A.

E, F, G <| B.
H, I, J <| C.
K, L, M <| D.

N, O <| E.
P, Q <| F.
R, S <| G.

T, U <| H.
   V <| I.
W, X <| J.

Y, Z <| K.
