theorem Th53:
  for N1,N2 being strict normal Subgroup of G holds the carrier of
  N1 "\/" N2 = N1 * N2
proof
  let N1,N2 be strict normal Subgroup of G;
  N1 * N2 = N2 * N1 by GROUP_3:125;
  hence thesis by Th51;
end;
