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

Label:
[f(a(),b()) -> c()] = 9
[a() -> a'()] = 1
[b() -> b'()] = 0
[c() -> f(a'(),b())] = 2
[c() -> f(a(),b'())] = 8
[c() -> f(a(),b())] = 4