theorem Th34:
  for X,Y being finite natural-membered set st X <> {} & X <N< Y
  holds (Sgm0 X).0 = (Sgm0 (X \/ Y)).0
proof
  let X,Y be finite natural-membered set;
  assume that
A1: X <> {} and
A2: X <N< Y;
  card X <> 0 by A1;
  then 0<len (Sgm0 X) by Th20;
  hence thesis by A2,Th29;
end;
