##
$unitslist_4 = "1001,1002,1003,1004,1101,1102,1103,1104,1201,1202,1203,1204,1301,1302,1303,1304,1401,1402,1403,1404,
1501,1502,1503,1504,1601,1602,1603,1604,1701,1702,1703,1704,1801,1802,1803,1804,1901,1902,1903,1904,2001,2002,2003,2004,
2101,2102,2103,2104,2201,2202,2203,2204,2301,2302,2303,2304,2401,2402,2403,2501,2502,2503,2504,2505";
unless ($digits_4 =~ /$unitslist/) {
$text =~ s{ ($digits_4) }
{$1}xmsg;
}