function checkform(f)
  {
  if(f.nome.value == '')
    {
    alert('Insert your name and surname');
    f.nome.focus();
    return false;
    }
  if(f.telefono.value == '')
    {
    alert('Insert your telephone number');
    f.nome.focus();
    return false;
    }  
  if(f.email.value == '')
    {
    alert('Insert your address');
    f.email.focus();
    return false;
    }
  if(f.email.value.search(/^([\w\.\-])+@(([\w\-]{2,})+\.)+([a-z0-9]{2,})+$/i) == -1)
    {
    alert('email format not correct');
	f.email.focus();
    return false;
    }
  if(f.richiesta.value == '')
    {
    alert('Insert a short description for your request');
    f.richiesta.focus();
    return false;
    }
  if(f.vericode.value != '')
    {
    alert('insert the control code that appear in the red box below');
    f.vericode.focus();
    return false;
    }
  return true;
}