function anularBotonDerecho() {
    if (event.button==2) {
alert('Botón derecho deshabilitado');
         }
  }
  document.onmousedown=anularBotonDerecho; 

function twoinone(nr){

if (nr==1){

parent.arriba.location.href="central.htm"

parent.central.location.href="arriba.htm"

}

if (nr==2){

parent.arriba.location.href="arriba.htm"

parent.central.location.href="central.htm"

}

}