The natural recursive definition of a Fibonacci function is a different beast.  The big issue with the naive and simple Fibonacci implementation is that it duplicates work, a ton of it.  The &#x27;map&#x27; above doesn&#x27;t have this issue.  To make Fibonacci efficient, it can be implemented as an iterative algorithm which isn&#x27;t too bad to read.  But there&#x27;s better news!  The recursive algorithm can be kept as-is, provided that the function is memoized, so that already computed values are cached.