theorem
  for M1 being Matrix of 0, n, D, M2 being Matrix of 0, m, D holds M1 = M2
proof
  let M1 be Matrix of 0, n, D, M2 be Matrix of 0, m, D;
  len M1 = 0 & len M2 = 0 by Def2;
  hence thesis by CARD_2:64;
end;
