“…{ definition of and zi ∈ X, 1 ≤ i ≤ n} σ(x, z 1 ); η(z 1 , y) + · · · + σ(x, z n ); η(z n , y), for all σ(x, z i ), η(z i , y) = 0, with 1 ≤ i ≤ n Clearly x = z i = y, using the definition of σ(x, y), for all σ ∈ T X×X . Thus, the proof follows directly from (13) for elements of T , as shown below.…”