We consider the following Problem:

  Strict Trs:
    {  concat(leaf(), Y) -> Y
     , concat(cons(U, V), Y) -> cons(U, concat(V, Y))
     , lessleaves(X, leaf()) -> false()
     , lessleaves(leaf(), cons(W, Z)) -> true()
     , lessleaves(cons(U, V), cons(W, Z)) ->
       lessleaves(concat(U, V), concat(W, Z))}
  StartTerms: basic terms
  Strategy: innermost

Certificate: YES(?,O(n^1))

Proof:
  We consider the following Problem:
  
    Strict Trs:
      {  concat(leaf(), Y) -> Y
       , concat(cons(U, V), Y) -> cons(U, concat(V, Y))
       , lessleaves(X, leaf()) -> false()
       , lessleaves(leaf(), cons(W, Z)) -> true()
       , lessleaves(cons(U, V), cons(W, Z)) ->
         lessleaves(concat(U, V), concat(W, Z))}
    StartTerms: basic terms
    Strategy: innermost
  
  Certificate: YES(?,O(n^1))
  
  Proof:
    The weightgap principle applies, where following rules are oriented strictly:
    
    TRS Component:
      {  lessleaves(X, leaf()) -> false()
       , lessleaves(leaf(), cons(W, Z)) -> true()}
    
    Interpretation of nonconstant growth:
    -------------------------------------
      The following argument positions are usable:
        Uargs(concat) = {}, Uargs(cons) = {2}, Uargs(lessleaves) = {1, 2}
      We have the following EDA-non-satisfying and IDA(1)-non-satisfying matrix interpretation:
      Interpretation Functions:
       concat(x1, x2) = [0 0] x1 + [1 0] x2 + [1]
                        [0 0]      [0 0]      [1]
       leaf() = [1]
                [0]
       cons(x1, x2) = [0 0] x1 + [1 0] x2 + [0]
                      [0 0]      [1 0]      [3]
       lessleaves(x1, x2) = [1 0] x1 + [1 0] x2 + [0]
                            [0 1]      [0 1]      [3]
       false() = [0]
                 [0]
       true() = [0]
                [0]
    
    The strictly oriented rules are moved into the weak component.
    
    We consider the following Problem:
    
      Strict Trs:
        {  concat(leaf(), Y) -> Y
         , concat(cons(U, V), Y) -> cons(U, concat(V, Y))
         , lessleaves(cons(U, V), cons(W, Z)) ->
           lessleaves(concat(U, V), concat(W, Z))}
      Weak Trs:
        {  lessleaves(X, leaf()) -> false()
         , lessleaves(leaf(), cons(W, Z)) -> true()}
      StartTerms: basic terms
      Strategy: innermost
    
    Certificate: YES(?,O(n^1))
    
    Proof:
      The weightgap principle applies, where following rules are oriented strictly:
      
      TRS Component: {concat(leaf(), Y) -> Y}
      
      Interpretation of nonconstant growth:
      -------------------------------------
        The following argument positions are usable:
          Uargs(concat) = {}, Uargs(cons) = {2}, Uargs(lessleaves) = {1, 2}
        We have the following EDA-non-satisfying and IDA(1)-non-satisfying matrix interpretation:
        Interpretation Functions:
         concat(x1, x2) = [0 0] x1 + [1 0] x2 + [1]
                          [0 0]      [0 1]      [1]
         leaf() = [0]
                  [0]
         cons(x1, x2) = [0 0] x1 + [1 0] x2 + [0]
                        [0 0]      [1 0]      [0]
         lessleaves(x1, x2) = [1 0] x1 + [1 0] x2 + [1]
                              [0 0]      [0 0]      [1]
         false() = [0]
                   [0]
         true() = [0]
                  [0]
      
      The strictly oriented rules are moved into the weak component.
      
      We consider the following Problem:
      
        Strict Trs:
          {  concat(cons(U, V), Y) -> cons(U, concat(V, Y))
           , lessleaves(cons(U, V), cons(W, Z)) ->
             lessleaves(concat(U, V), concat(W, Z))}
        Weak Trs:
          {  concat(leaf(), Y) -> Y
           , lessleaves(X, leaf()) -> false()
           , lessleaves(leaf(), cons(W, Z)) -> true()}
        StartTerms: basic terms
        Strategy: innermost
      
      Certificate: YES(?,O(n^1))
      
      Proof:
        The weightgap principle applies, where following rules are oriented strictly:
        
        TRS Component:
          {lessleaves(cons(U, V), cons(W, Z)) ->
           lessleaves(concat(U, V), concat(W, Z))}
        
        Interpretation of nonconstant growth:
        -------------------------------------
          The following argument positions are usable:
            Uargs(concat) = {}, Uargs(cons) = {2}, Uargs(lessleaves) = {1, 2}
          We have the following EDA-non-satisfying and IDA(1)-non-satisfying matrix interpretation:
          Interpretation Functions:
           concat(x1, x2) = [0 0] x1 + [1 0] x2 + [1]
                            [0 0]      [0 1]      [1]
           leaf() = [0]
                    [0]
           cons(x1, x2) = [0 0] x1 + [1 0] x2 + [2]
                          [0 0]      [1 0]      [0]
           lessleaves(x1, x2) = [1 0] x1 + [1 0] x2 + [1]
                                [0 0]      [0 0]      [1]
           false() = [0]
                     [0]
           true() = [0]
                    [0]
        
        The strictly oriented rules are moved into the weak component.
        
        We consider the following Problem:
        
          Strict Trs: {concat(cons(U, V), Y) -> cons(U, concat(V, Y))}
          Weak Trs:
            {  lessleaves(cons(U, V), cons(W, Z)) ->
               lessleaves(concat(U, V), concat(W, Z))
             , concat(leaf(), Y) -> Y
             , lessleaves(X, leaf()) -> false()
             , lessleaves(leaf(), cons(W, Z)) -> true()}
          StartTerms: basic terms
          Strategy: innermost
        
        Certificate: YES(?,O(n^1))
        
        Proof:
          The weightgap principle applies, where following rules are oriented strictly:
          
          TRS Component: {concat(cons(U, V), Y) -> cons(U, concat(V, Y))}
          
          Interpretation of nonconstant growth:
          -------------------------------------
            The following argument positions are usable:
              Uargs(concat) = {}, Uargs(cons) = {2}, Uargs(lessleaves) = {1, 2}
            We have the following EDA-non-satisfying and IDA(1)-non-satisfying matrix interpretation:
            Interpretation Functions:
             concat(x1, x2) = [0 1] x1 + [1 0] x2 + [0]
                              [0 1]      [0 1]      [0]
             leaf() = [0]
                      [0]
             cons(x1, x2) = [0 1] x1 + [1 0] x2 + [0]
                            [0 1]      [0 1]      [1]
             lessleaves(x1, x2) = [1 0] x1 + [1 0] x2 + [1]
                                  [0 0]      [0 0]      [1]
             false() = [0]
                       [0]
             true() = [0]
                      [0]
          
          The strictly oriented rules are moved into the weak component.
          
          We consider the following Problem:
          
            Weak Trs:
              {  concat(cons(U, V), Y) -> cons(U, concat(V, Y))
               , lessleaves(cons(U, V), cons(W, Z)) ->
                 lessleaves(concat(U, V), concat(W, Z))
               , concat(leaf(), Y) -> Y
               , lessleaves(X, leaf()) -> false()
               , lessleaves(leaf(), cons(W, Z)) -> true()}
            StartTerms: basic terms
            Strategy: innermost
          
          Certificate: YES(O(1),O(1))
          
          Proof:
            We consider the following Problem:
            
              Weak Trs:
                {  concat(cons(U, V), Y) -> cons(U, concat(V, Y))
                 , lessleaves(cons(U, V), cons(W, Z)) ->
                   lessleaves(concat(U, V), concat(W, Z))
                 , concat(leaf(), Y) -> Y
                 , lessleaves(X, leaf()) -> false()
                 , lessleaves(leaf(), cons(W, Z)) -> true()}
              StartTerms: basic terms
              Strategy: innermost
            
            Certificate: YES(O(1),O(1))
            
            Proof:
              Empty rules are trivially bounded

Hurray, we answered YES(?,O(n^1))