theorem Th10:
  (ComplexFuncAdd(A)).(ComplexFuncZero(A),f) = f
proof
  now
    let x be Element of A;
    thus ((ComplexFuncAdd(A)).(ComplexFuncZero(A),f)).x = (ComplexFuncZero(A))
    .x + f.x by Th1
      .= 0c + f.x by FUNCOP_1:7
      .= f.x;
  end;
  hence thesis by FUNCT_2:63;
end;
