Input TRS:
    1: active(f(X,X)) -> mark(f(a(),b()))
    2: active(b()) -> mark(a())
    3: mark(f(X1,X2)) -> active(f(mark(X1),X2))
    4: mark(a()) -> active(a())
    5: mark(b()) -> active(b())
    6: f(mark(X1),X2) -> f(X1,X2)
    7: f(X1,mark(X2)) -> f(X1,X2)
    8: f(active(X1),X2) -> f(X1,X2)
    9: f(X1,active(X2)) -> f(X1,X2)
Number of Rules: 9
Direct QWPOS(Sum) ... failed.