YES(?,O(n^2))

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

Proof:
 Complexity Transformation Processor:
  strict:
   f(a(),f(f(a(),x),a())) -> f(f(a(),f(a(),x)),a())
  weak:
   
  Matrix Interpretation Processor:
   dimension: 2
   max_matrix:
    [1 1]
    [0 1]
    interpretation:
                        [1 1]  
     [f](x0, x1) = x0 + [0 1]x1,
     
           [0]
     [a] = [1]
    orientation:
                              [1 2]    [3]    [1 2]    [2]                         
     f(a(),f(f(a(),x),a())) = [0 1]x + [3] >= [0 1]x + [3] = f(f(a(),f(a(),x)),a())
    problem:
     strict:
      
     weak:
      f(a(),f(f(a(),x),a())) -> f(f(a(),f(a(),x)),a())
    Qed