YES

Problem:
 f(f(a(),f(x,a())),a()) -> f(a(),f(f(x,a()),a()))

Proof:
 DP Processor:
  DPs:
   f#(f(a(),f(x,a())),a()) -> f#(f(x,a()),a())
   f#(f(a(),f(x,a())),a()) -> f#(a(),f(f(x,a()),a()))
  TRS:
   f(f(a(),f(x,a())),a()) -> f(a(),f(f(x,a()),a()))
  ADG Processor:
   DPs:
    f#(f(a(),f(x,a())),a()) -> f#(f(x,a()),a())
    f#(f(a(),f(x,a())),a()) -> f#(a(),f(f(x,a()),a()))
   TRS:
    f(f(a(),f(x,a())),a()) -> f(a(),f(f(x,a()),a()))
   graph:
    f#(f(a(),f(x,a())),a()) -> f#(f(x,a()),a()) ->
    f#(f(a(),f(x,a())),a()) -> f#(f(x,a()),a())
    f#(f(a(),f(x,a())),a()) -> f#(f(x,a()),a()) ->
    f#(f(a(),f(x,a())),a()) -> f#(a(),f(f(x,a()),a()))
   Restore Modifier:
    DPs:
     f#(f(a(),f(x,a())),a()) -> f#(f(x,a()),a())
     f#(f(a(),f(x,a())),a()) -> f#(a(),f(f(x,a()),a()))
    TRS:
     f(f(a(),f(x,a())),a()) -> f(a(),f(f(x,a()),a()))
    SCC Processor:
     #sccs: 1
     #rules: 1
     #arcs: 2/4
     DPs:
      f#(f(a(),f(x,a())),a()) -> f#(f(x,a()),a())
     TRS:
      f(f(a(),f(x,a())),a()) -> f(a(),f(f(x,a()),a()))
     Matrix Interpretation Processor:
      dimension: 1
      interpretation:
       [f#](x0, x1) = x0 + x1,
       
       [f](x0, x1) = x0 + x1,
       
       [a] = 1
      orientation:
       f#(f(a(),f(x,a())),a()) = x + 3 >= x + 2 = f#(f(x,a()),a())
       
       f(f(a(),f(x,a())),a()) = x + 3 >= x + 3 = f(a(),f(f(x,a()),a()))
      problem:
       DPs:
        
       TRS:
        f(f(a(),f(x,a())),a()) -> f(a(),f(f(x,a()),a()))
      Qed