Q: I'm having trouble getting started with assignment 4. What do I do?
A: Here is a simple hint for you.
a) Start with input={A,B} where A knows B.
b) Consider that CROSS input,input gives you {A,B,C,D} where
(A,B) is in input and (C,D) is in input.
c) If we filter, group, and count this properly, we have
one solution.
This, however, is a really inefficient solution, and it is possible
to do much better.