
theorem Th25:
  for A being non empty RelStr, a1,a2 being Element of A st
    A is strongly_connected holds
      a1 <= a2 or a2 <= a1
proof
  let A be non empty RelStr;
  let a1, a2 be Element of A;
  assume A is strongly_connected;
  then [a1,a2] in the InternalRel of A or [a2,a1] in the InternalRel of A
    by RELAT_2:def 7;
  hence a1 <= a2 or a2 <= a1 by ORDERS_2:def 5;
end;
