YES

---- CR(R)
---- [Knuth and Bendix, 1970]
R:
f(f(f(x))) -> a()
f(f(a())) -> a()
f(a()) -> a()
f(f(g(g(x)))) -> f(a())
g(f(a())) -> a()
g(a()) -> a()
CP(R):
f(a()) -> a()
f(f(a())) -> a()
f(a()) -> a()
f(f(a())) -> a()
f(f(a())) -> a()
f(a()) -> a()
g(a()) -> a()
f(f(a())) -> a()
f(f(f(a()))) -> a()
f(f(g(a()))) -> f(a())
f(f(g(a()))) -> f(a())