Consider the following piece of code:

def f(x):
    if x == 0 or x == 1:
        return x
    return f(x - 1) + f(x - 2)

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Part A (1 point)

Describe, in words, what this code does, and how it does it.

This function computes the fibonnaci sequence using recursion. The base cases are $x=0$ and $x=1$, in which case the function will return 0 or 1, respectively. In all other cases, the function will call itself to find the $x-1$ and $x-2$ fibonnaci numbers, and then add them together.

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Part B (2 points)

For what inputs will this function not behave as expected? What will happen?

The function will not work correctly for inputs less than zero. Such inputs will result in an infinite recursion, as the function will keep subtracting one but never reach a base case that stops it.