function ChangeMonth(m,y){
  cal = document.getElementById("calendar");
  if (cal){
    var req = new JsHttpRequest();
    req.onreadystatechange = function() {
      if (req.readyState == 4) {
        if (req.responseJS.info && req.responseJS.info.length > 0){
          cal.innerHTML = req.responseJS.info;
        }
      } else if (req.readyState == 3){
      }
    }
    req.open(null, 'get_calendar.php', true);
    req.send( { 'm': m, 'y': y } );
  }
}