theorem
  for a being non zero Element of F_Real
  holds (homography(a*N1)).P = (homography(N1)).P
  proof
    let a be non zero Element of F_Real;
    set M = a * 1.(F_Real,3);
    thus (homography(a*N1)).P = (homography(M * N1)).P by Th02
                      .= (homography(M)).((homography(N1)).P) by Th14
                      .= (homography(N1)).(P) by Th17;
  end;
