function SingleImgOn (name, img) {
  document[name].src = eval(img + "_on.src");
}
function SingleImgOff (name, img) {
  document[name].src = eval(img + "_off.src");
}
function ImgOn (img){
  document[img].src = eval(img + "_on.src");
}
function ImgOff (img){
  document[img].src = eval(img + "_off.src");
}
function ChangeClass (element, class_name) {
  element.className = class_name;
}