YES
TRS:
 {f(a(), f(a(), x)) -> f(a(), f(f(a(), a()), f(a(), x)))}
 DP:
  Strict:
   {f#(a(), f(a(), x)) -> f#(f(a(), a()), f(a(), x)),
    f#(a(), f(a(), x)) -> f#(a(), f(f(a(), a()), f(a(), x))),
    f#(a(), f(a(), x)) -> f#(a(), a())}
  Weak:
  {f(a(), f(a(), x)) -> f(a(), f(f(a(), a()), f(a(), x)))}
  EDG:
   {}
   SCCS:
    
    Qed