Input TRS:
    1: f(f(a(),b()),x) -> f(a(),f(a(),x))
    2: f(f(b(),a()),x) -> f(b(),f(b(),x))
    3: f(x,f(y,z)) -> f(f(x,y),z)
Number of Rules: 3
Direct QWPOS(mSum) ... failed.