🚀 go-pugleaf

Hi folks.

I am trying to teach myself prolog, and I am having a problem.  I
programmed a fibonacci number finder.

  fib(1,1).            /* fib(S,N) where N is the Sth fibonacci # */
  fib(2,1).
  fib(S,N) :- S>2,
              A is S-1,
              B is S-2,
              fib(A,C),
              fib(B,D),
              N is C+D.

but all I get when I try to ask fib(5,X) is error: free variable in
expression.  But there is stuff like this in C&M's book!  How do I
get the 5th fib. number?

second question: how do I get the second element of a list?
[A|B|C]?  where B is second element?  or maybe [A|[B|C]]?

thanks in advance!
*dt*