database of social networking in prolog

I am currently building a social networking stuff, similar like facebook or friendster and  I  a bit stuck in this part where I need to have a predicate that basically says " who is X friends with, through at most two intermediate people, and what is the path?" I have a database in my prolog file which is something like:

fr(chris, geen).
fr(geen,jill).
fr(jill, clark).

I want to create a prolog predicate called friend(X,Y,Z). An example I want it to do something like

friend(chris,clark,L).
L = [chris, geen, jill, clark].
....
and other stuff according what it finds in the database.

I know that I am suppose to use recursion here and backtracking, as well as the cut operation to tell the function to stop when it finds a friend more than 2 bridges. Can someone please help me one this
kuntilanakAsked:
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Kent OlsenData Warehouse Architect / DBACommented:
In database terms, you'll want to join two friends together, then join all of the friends of one of them.

Friend A has 10 friends, one of which is B.
Freind B has 15 friends, two of which are A and C.  It doesn't matter if C is a friend of A.

Join all of the friends of A and B.  To this list join all of the friends of C.  Friend A is now joined to the friends of C.


Kent
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kuntilanakAuthor Commented:
can you help me to code that a bit in prolog.. cause that's where my confusion is
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