Input TRS:
    1: f(x,a(b(c(y)))) -> f(b(c(a(b(x)))),y)
    2: f(a(x),y) -> f(x,a(y))
    3: f(b(x),y) -> f(x,b(y))
    4: f(c(x),y) -> f(x,c(y))
Number of Rules: 4
Direct QLPOS ... failed.