function checkSearch(form) {
  if(form.g.selectedIndex < 1) {
    alert('Kies een gemeente');
    form.g.focus();
    return false;
  }
  if(form.n.value == '') {
    form.n.disabled = true;
  }
  if(form.p.value == '') {
    form.p.disabled = true;
  }
  return true;
}