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