YES

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

Proof:
 Uncurry Processor:
  a3(x,a(),x4) -> f(a3(a1(a()),x,a()),x4)
  a2(x,a()) -> a3(a1(a()),x,a())
  f(a2(x2,x1),x3) -> a3(x2,x1,x3)
  f(a1(x2),x3) -> a2(x2,x3)
  f(a(),x3) -> a1(x3)
  Matrix Interpretation Processor: dim=3
   
   interpretation:
               [1 0 0]     [0]
    [a1](x0) = [0 0 0]x0 + [0]
               [0 0 1]     [1],
    
                       [1 0 0]     [1 0 0]     [1 0 0]  
    [a3](x0, x1, x2) = [0 0 0]x0 + [0 0 0]x1 + [1 0 0]x2
                       [1 0 0]     [0 0 0]     [1 0 1]  ,
    
                   [1 0 0]     [1 0 0]  
    [a2](x0, x1) = [0 0 0]x0 + [0 0 0]x1
                   [0 0 0]     [0 0 0]  ,
    
                  [1 0 1]     [1 0 0]  
    [f](x0, x1) = [0 0 0]x0 + [1 0 0]x1
                  [1 1 1]     [1 0 1]  ,
    
          [0]
    [a] = [1]
          [0]
   orientation:
                   [1 0 0]    [1 0 0]      [1 0 0]    [1 0 0]                            
    a3(x,a(),x4) = [0 0 0]x + [1 0 0]x4 >= [0 0 0]x + [1 0 0]x4 = f(a3(a1(a()),x,a()),x4)
                   [1 0 0]    [1 0 1]      [1 0 0]    [1 0 1]                            
    
                [1 0 0]     [1 0 0]                     
    a2(x,a()) = [0 0 0]x >= [0 0 0]x = a3(a1(a()),x,a())
                [0 0 0]     [0 0 0]                     
    
                      [1 0 0]     [1 0 0]     [1 0 0]      [1 0 0]     [1 0 0]     [1 0 0]                 
    f(a2(x2,x1),x3) = [0 0 0]x1 + [0 0 0]x2 + [1 0 0]x3 >= [0 0 0]x1 + [0 0 0]x2 + [1 0 0]x3 = a3(x2,x1,x3)
                      [1 0 0]     [1 0 0]     [1 0 1]      [0 0 0]     [1 0 0]     [1 0 1]                 
    
                   [1 0 1]     [1 0 0]     [1]    [1 0 0]     [1 0 0]              
    f(a1(x2),x3) = [0 0 0]x2 + [1 0 0]x3 + [0] >= [0 0 0]x2 + [0 0 0]x3 = a2(x2,x3)
                   [1 0 1]     [1 0 1]     [1]    [0 0 0]     [0 0 0]              
    
                [1 0 0]     [0]    [1 0 0]     [0]         
    f(a(),x3) = [1 0 0]x3 + [0] >= [0 0 0]x3 + [0] = a1(x3)
                [1 0 1]     [1]    [0 0 1]     [1]         
   problem:
    a3(x,a(),x4) -> f(a3(a1(a()),x,a()),x4)
    a2(x,a()) -> a3(a1(a()),x,a())
    f(a2(x2,x1),x3) -> a3(x2,x1,x3)
    f(a(),x3) -> a1(x3)
   Matrix Interpretation Processor: dim=3
    
    interpretation:
                [1 0 0]  
     [a1](x0) = [0 0 0]x0
                [0 0 0]  ,
     
                        [1 0 0]     [1 0 0]     [1 0 1]  
     [a3](x0, x1, x2) = [1 0 0]x0 + [0 0 0]x1 + [0 0 0]x2
                        [1 0 0]     [0 0 0]     [0 0 0]  ,
     
                    [1 0 0]     [1 0 1]     [0]
     [a2](x0, x1) = [0 0 0]x0 + [0 0 0]x1 + [1]
                    [0 1 0]     [0 1 0]     [0],
     
                   [1 1 0]     [1 0 1]  
     [f](x0, x1) = [1 0 1]x0 + [0 0 0]x1
                   [1 0 0]     [0 0 0]  ,
     
           [0]
     [a] = [0]
           [0]
    orientation:
                    [1 0 0]    [1 0 1]      [1 0 0]    [1 0 1]                            
     a3(x,a(),x4) = [1 0 0]x + [0 0 0]x4 >= [1 0 0]x + [0 0 0]x4 = f(a3(a1(a()),x,a()),x4)
                    [1 0 0]    [0 0 0]      [1 0 0]    [0 0 0]                            
     
                 [1 0 0]    [0]    [1 0 0]                     
     a2(x,a()) = [0 0 0]x + [1] >= [0 0 0]x = a3(a1(a()),x,a())
                 [0 1 0]    [0]    [0 0 0]                     
     
                       [1 0 1]     [1 0 0]     [1 0 1]     [1]    [1 0 0]     [1 0 0]     [1 0 1]                 
     f(a2(x2,x1),x3) = [1 1 1]x1 + [1 1 0]x2 + [0 0 0]x3 + [0] >= [0 0 0]x1 + [1 0 0]x2 + [0 0 0]x3 = a3(x2,x1,x3)
                       [1 0 1]     [1 0 0]     [0 0 0]     [0]    [0 0 0]     [1 0 0]     [0 0 0]                 
     
                 [1 0 1]      [1 0 0]           
     f(a(),x3) = [0 0 0]x3 >= [0 0 0]x3 = a1(x3)
                 [0 0 0]      [0 0 0]           
    problem:
     a3(x,a(),x4) -> f(a3(a1(a()),x,a()),x4)
     a2(x,a()) -> a3(a1(a()),x,a())
     f(a(),x3) -> a1(x3)
    Matrix Interpretation Processor: dim=3
     
     interpretation:
                 [1 0 0]  
      [a1](x0) = [0 0 0]x0
                 [0 0 0]  ,
      
                         [1 1 0]     [1 1 0]     [1 0 0]  
      [a3](x0, x1, x2) = [0 0 0]x0 + [0 0 0]x1 + [0 0 0]x2
                         [0 0 0]     [0 0 0]     [0 0 0]  ,
      
                     [1 1 1]     [1 1 0]  
      [a2](x0, x1) = [0 1 1]x0 + [0 0 0]x1
                     [0 0 1]     [0 0 0]  ,
      
                    [1 0 0]     [1 0 0]  
      [f](x0, x1) = [0 0 0]x0 + [0 0 0]x1
                    [0 0 0]     [0 0 0]  ,
      
            [0]
      [a] = [1]
            [0]
     orientation:
                     [1 1 0]    [1 0 0]     [1]    [1 1 0]    [1 0 0]                            
      a3(x,a(),x4) = [0 0 0]x + [0 0 0]x4 + [0] >= [0 0 0]x + [0 0 0]x4 = f(a3(a1(a()),x,a()),x4)
                     [0 0 0]    [0 0 0]     [0]    [0 0 0]    [0 0 0]                            
      
                  [1 1 1]    [1]    [1 1 0]                     
      a2(x,a()) = [0 1 1]x + [0] >= [0 0 0]x = a3(a1(a()),x,a())
                  [0 0 1]    [0]    [0 0 0]                     
      
                  [1 0 0]      [1 0 0]           
      f(a(),x3) = [0 0 0]x3 >= [0 0 0]x3 = a1(x3)
                  [0 0 0]      [0 0 0]           
     problem:
      f(a(),x3) -> a1(x3)
     Matrix Interpretation Processor: dim=3
      
      interpretation:
                  [1 0 0]  
       [a1](x0) = [0 0 0]x0
                  [0 0 0]  ,
       
                     [1 1 0]     [1 0 0]  
       [f](x0, x1) = [0 0 0]x0 + [0 0 0]x1
                     [0 0 0]     [0 0 0]  ,
       
             [0]
       [a] = [1]
             [0]
      orientation:
                   [1 0 0]     [1]    [1 0 0]           
       f(a(),x3) = [0 0 0]x3 + [0] >= [0 0 0]x3 = a1(x3)
                   [0 0 0]     [0]    [0 0 0]           
      problem:
       
      Qed