function f(tdName) {
  var td = document.getElementById(tdName);
  td.style.background="#446666";
}

function fo(tdName) {
  var td = document.getElementById(tdName);
  td.style.background="transparent";
}

function mOn (imageName) {
  document.images[imageName].src=eval(imageName + "_on.src");
}

function mOf (imageName) {
  document.images[imageName].src=eval(imageName + "_of.src");
}