YES

---- CR(R)
---- Hot decreasingness.
R:
f(a(),a()) -> b()
a() -> a'()
f(a'(),x) -> f(x,x)
f(x,a'()) -> f(x,x)
f(a'(),a'()) -> b()
b() -> f(a'(),a'())

C:


Label:
[f(a(),a()) -> b()] = 1
[a() -> a'()] = 1
[f(a'(),x) -> f(x,x)] = 0
[f(x,a'()) -> f(x,x)] = 0
[f(a'(),a'()) -> b()] = 0
[b() -> f(a'(),a'())] = 0