Input TRS:
    1: active(f(a(),X,X)) -> mark(f(X,b(),b()))
    2: active(b()) -> mark(a())
    3: mark(f(X1,X2,X3)) -> active(f(X1,mark(X2),X3))
    4: mark(a()) -> active(a())
    5: mark(b()) -> active(b())
    6: f(mark(X1),X2,X3) -> f(X1,X2,X3)
    7: f(X1,mark(X2),X3) -> f(X1,X2,X3)
    8: f(X1,X2,mark(X3)) -> f(X1,X2,X3)
    9: f(active(X1),X2,X3) -> f(X1,X2,X3)
    10: f(X1,active(X2),X3) -> f(X1,X2,X3)
    11: f(X1,X2,active(X3)) -> f(X1,X2,X3)
Number of Rules: 11
Direct QWPOS(mSum) ... failed.