How is this algorithm working?! Can someone explain it to me please..have an interview tomorrow
<pre><code>def sum_in(numbers, sum_):
    """whether any two numbers from `numbers` form `sum_`."""
    return any((sum_-n) in numbers for n in numbers)
</code></pre>

<p>It basically takes a list, and checks if any two numbers from it form a sum equalling sum_. I can't seem to get how that sum_-n verifies that TWO numbers equal the sum. Wouldn't it just be checking with one n each loop?!</p>
