function ZmenaKategorie( lib_lbl ) {
    var da=document.F.id_skupina_kat.options[document.F.id_skupina_kat.selectedIndex].value;
    var out = '<div class="CHECKBOX-LIST-ITEM"><input name="id_kategorie" value="--" checked onclick="libovolny_checkbox( this );" type="checkbox">' + lib_lbl + '</div>';
    
    if (da>0) {
        var pocet = 0;
        for(jp=0; jp<Akat_nazev.length; ++jp) 
            if (Aid_skupina_kat[jp]==da) {
                itm = '<div class="CHECKBOX-LIST-ITEM">';
                itm = itm + '<input name="id_kategorie" value="' + Aid_kategorie[jp] + '" onclick="libovolny_checkbox( this );" type="checkbox">';
                itm = itm + Akat_nazev[jp] + '</div>';
                out=out + itm;
                pocet++;
            }
        if (pocet<2) 
            out = '';
        document.getElementById('CHECKBOXES-ID-KATEGORIE').innerHTML=out;
    } else {
        document.getElementById('CHECKBOXES-ID-KATEGORIE').innerHTML='';
    }
}