function $(id) {
  if (document.getElementById(id))
    return document.getElementById(id);
  else
    return null;
}

function showDiv(id) {
  $(id).style.display = 'block';
}

function hideDiv(id) {
  $(id).style.display = 'none';
}

function loadNixCSS(filename) {
  if ((navigator.userAgent.indexOf("Linux") != -1)||(navigator.userAgent.indexOf("Unix") != -1))
    document.write('<link href="' + filename + '" rel="stylesheet" type="text/css" />');
}