Input TRS:
    1: p(f(f(x))) -> q(f(g(x)))
    2: p(g(g(x))) -> q(g(f(x)))
    3: q(f(f(x))) -> p(f(g(x)))
    4: q(g(g(x))) -> p(g(f(x)))
Number of Rules: 4
Direct POLO(Sum) ... failed.