
theorem Th13:
  for L being RelStr st L is empty holds L is bounded
proof
  let L be RelStr such that
A1: L is empty;
  set x = the Element of L;
  thus L is lower-bounded
  proof
    take x;
    let a be Element of L;
    assume a in the carrier of L;
    hence thesis by A1;
  end;
  take x;
  let a be Element of L;
  assume a in the carrier of L;
  hence thesis by A1;
end;
