(Kroening/Strichman: Kapitel 10)
(x2x1) (x1 - x3x2) (x30) f (f (x1) - f (x2)) f (x3)
f (a[32], b[1]) = f (b[32], a[1]) a[32] = b[32]
x = v{i : = e}[j] y = v[j] x > ex > y