Input TRS:
    1: a__f(X) -> g(h(f(X)))
    2: mark(f(X)) -> a__f(mark(X))
    3: mark(g(X)) -> g(X)
    4: mark(h(X)) -> h(mark(X))
    5: a__f(X) -> f(X)
Number of Rules: 5
Direct QKBOS(Sum) ... failed.