reserve fi,psi for Ordinal-Sequence,
  A,A1,B,C,D for Ordinal,
  X,Y for set,
  x,y for object;

theorem Th68:
  B <> {} implies A*^B div^ B = A
proof
  assume B <> {};
  then
A1: {} in B by Th8;
  A*^B = A*^B+^{} by ORDINAL2:27;
  hence thesis by A1,Def6;
end;
