YES

---- CR(R)
---- Rule Labeling [van Oostrom, RTA 2008].
R:
a() -> b()
a() -> f(a())
b() -> f(f(b()))
f(f(f(b()))) -> b()

Label:
[a() -> b()] = 5
[a() -> f(a())] = 0
[b() -> f(f(b()))] = 0
[f(f(f(b()))) -> b()] = 0