function submit_form() {
  var form = document.getElementsByTagName('form')[0];
  form.submit();
}
function submit_form_back() {
  var form = document.getElementsByTagName('form')[0];
  var hidden = document.createElement('input');
  hidden.type = 'hidden';
  hidden.name = 'back';
  hidden.value = 'back';
  form.appendChild(hidden);
  form.submit();
}
function clear_form(){
  Form.reset('search_form');
}