13 For any integer n, fib(n) returns the Fibonacci number with index n.
14 This may be defined by fib(0) = 0, fib(1) = 1 and for any n (positive
15 or negative) fib(n) = fib(n-1) + fib(n-2).
18 > print fib(-2), fib(-1), fib(0), fib(1), fib(2), fib(3), fib(4), fib(5)
25 NUMBER *qfib(NUMBER *n)