YES
Input TRS:
    1: a() -> b()
    2: f(a()) -> b()
    3: g(x) -> g(a()) | f(x) --> x
Infeasibility test:
    f(x) --> x
Co-Order(NegReal,≥,Sum) ... succeeded.
     a()	weight: (- (/ 1 2))
     b()	weight: -1
     f(x1)	weight: (- (/ 1 2)) + x1
    #(x1)	weight: x1
     g(x1)	weight: x1