Choosing tools

We saw from his laureate document that Walter Kohn's country of birth was "Austria" and that his prize affiliation country was "USA". If we want to count the number of laureates born in Austria with a prize affiliation country that is not also Austria, what MongoDB concepts/tools should we use?

(The nobel database is available in the console as db, and the Walter's Kohn document is available to you as doc. Feel free to examine the structure of the document doc in the console, and play around with database queries!)