function overImg(name) {
  var img_src = document[name].src;
  var img_pos = img_src.lastIndexOf(".");
  document[name].src = img_src.slice(0,img_pos)+"_r.gif";
}

function outImg(name) {
  var img_src = document[name].src;
  var img_pos = img_src.lastIndexOf("_");
  document[name].src = img_src.slice(0,img_pos)+".gif";
}