Added HW after fixing git issues.

2 files added.
That's not exactly how `assert` works. `assert` is a statement that throws an error if the expression(s) following it do not evaluate to True. `assert` will not enforce any restrictions on the input to those functions. 

This assert statement doesn't cause an AssertionError because a function is considered greater than most (all?) integers. For this assignment, we're using assert statements to act as unit tests. We want to know if the function produces the expected output for a given input. Something like this:

    if __name__ == "__main__":
        # assert function(input) == expected
        # ...
        assert fibonacci(7) == 13
        # ...
        assert lucas(4) == 7
        # ...
        assert sum_series(4, 2, 1) == lucas(4)
        # ...
        print('all tests passed!')

The above code isn't ideal as it involves a lot of repetition.