Regarding exercise sheet 10
You must not take a shortcut with the domain name of a name server, e.g., you have to use
dig @18.104.22.168 saarland NS
dig @a.root-servers.net saarland NS
This will yield less points in the exercise. If you already have the NS, e.g., for a given TLD, you do not have to query the root name server again.