MAYBE
Input TRS:
    1: a() -> b()
    2: f(x) -> c() | x --> a()
Infeasibility test:
    f(b()) --> x
    c() --> x
Co-Order(NegReal,≥,Sum) ...Co-QLPOpS ...Co-QWPOpS(PosReal,>,Sum) ...Co-Order(PosReal,≥,Sum-Sum; PosReal,≥,Sum-Sum) ...failed.