function pruefen() {

var f1  = document.formular.strasse.value;
var f2  = document.formular.postfach.value;
var f3  = document.formular.ort.value;
var f4  = document.formular.plz.value;
var f5  = document.formular.email.value;
var f6  = document.formular.anzahl.value;

/*****/

if(f1.length < 2) {
    alert('Please enter your adress!\t');
    document.formular.strasse.select();
    document.formular.strasse.focus();
    return false;
}

/*****/

if(f2 == f4) {
    alert('The Post office box can\'t be the same as the ZIP code!');
    document.formular.postfach.select();
    document.formular.postfach.focus();
    return false;
}


/*****/

if(f3.length < 2) {
    alert('Please enter your city!\t');
    document.formular.ort.select();
    document.formular.ort.focus();
    return false;
}

/*****/

if(f4.length < 2) {
    alert('Please enter your ZIP code!\t');
    document.formular.plz.select();
    document.formular.plz.focus();
    return false;
}

/*****/

if(/^[_a-z0-9-]+(\.[_a-z0-9-]+)*@([a-z0-9-]+\.)+([a-z]{2,4})$/i.test(f5) == false) {
    alert('Your Email address is invalid!\t');
    document.formular.email.select();
    document.formular.email.focus();
    return false;
}

/*****/

if(/^[1-5]$/.test(f6) == false) {
    alert('The field number of license are empty!\t');
    document.formular.anzahl.select();
    document.formular.anzahl.focus();
    return false;
}

/*****/

if (document.formular.datenschutz.checked == false)
{
    alert('Bitte lesen Sie die Datenschutzerklärung!\t');
    return false;
}

/*****/

document.formular.submit.disabled = true;
return true;

}