a(c(x)) -> e(a(x))
a(d(x)) -> v(a(x))
e(b(x)) -> b(c(x))
v(b(x)) -> b(d(x))
u(x) -> d(w(x))
c(w(x)) -> d(w(x))
e(a(w(x))) -> b(d(w(x)))
v(a(w(x))) -> b(d(w(x)))