reserve i,n,m,k,x for Nat,
  i1,i2 for Integer;

theorem Th8:
  for e being set st e in k-SD_Sub holds e is Integer
proof
  let e be set;
  assume e in k-SD_Sub;
  then
  ex t be Element of INT st e = t & t >= -Radix(k-'1)-1 & t <= Radix(k-'1);
  hence thesis;
end;
