theorem Th12:
  i1 in k-SD implies i1 <= Radix(k)-1 & i1 >= -Radix(k)+1
proof
  assume i1 in k-SD;
  then
  ex i be Element of INT st i = i1 & i <= Radix(k)-1 & i >= -Radix(k)+1;
  hence thesis;
end;
