theorem Th31:
  for N1,N2 being strict normal StableSubgroup of G holds the
  carrier of N1 "\/" N2 = N1 * N2
proof
  let N1,N2 be strict normal StableSubgroup of G;
  N1 * N2 = N2 * N1 by Th28;
  hence thesis by Th30;
end;
