function load(obj, imga, imgn) {
  if (document.images) {
    (document.images[obj+"-n"] = new Image()).src = '/img/common/'+imgn;
    (document.images[obj+"-a"] = new Image()).src = '/img/common/'+imga;
  }
}

function on(obj) {
  if (document.images) document.images[obj].src = document.images[obj+"-a"].src;
}

function off(obj) {
  if (document.images) document.images[obj].src = document.images[obj+"-n"].src;
}