LISP is the only pure language, ban everything else. Especially Smalltalk and Ada.
/s
LISP is stupid. I hated that damn course in college. CAR CAR CDR CDR CAR CAR *THIS*.
If we're banning things on non-purity, then Smalltalk, as the only pure object oriented language, should stay. Java and all others should go. I'd like to say ban Ada on principle because it is the only American computer language developed by the government. But there have been a couple of good things developed from it. It is one of the most "provably correct" languages.
You can ban all C derived languages after C though.