Apex domains cannot have CNAME records.
Question and response
Question
dig lth.se. NS
Answer
lth.se. 5 NS b.ns.kth.se.
lth.se. 5 NS nic.lth.se.
lth.se. 5 NS nic2.lth.se.
Authority
The response has no authority records.
Additional
b.ns.kth.se. 5 A 130.237.72.250
nic.lth.se. 5 A 130.235.20.3
nic2.lth.se. 5 A 130.235.20.5
b.ns.kth.se. 5 AAAA 2001:6b0:1:0:0:0:0:250
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0