static String bitSetToString( ArrayList<Version> sigla, 
        ArrayList<Group> groups, BitSet bs )
    {
        try
        {
            StringBuilder sb = new StringBuilder();
            for ( int i = bs.nextSetBit(0); i>= 0; i = bs.nextSetBit(i+1))
            {
                Version v = sigla.get(i-1);
                String siglum = v.shortName;
                if ( isLayerName(siglum) )
                {
                    Group g = groups.get(v.group-1);
                    siglum = g.name+"/"+v.shortName;
                }
                if ( sb.length()>0 )
                    sb.append( " " );
                sb.append( siglum );
            }
            return sb.toString();
        }
        catch ( Exception e )
        {
            System.out.println("error");
            return "";
        }
    }