A question on a quiz asked which value in [12, 13, 14, 15] is the first assigned to `right sorted`

. Apparently the answer was 13, I thought is was 14. Could you explain how?

```
def merge_sort(items):
if len(items) <= 1:
return items
middle_index = len(items) // 2
left_split = items[:middle_index]
right_split = items[middle_index:]
left_sorted = merge_sort(left_split)
right_sorted = merge_sort(right_split)
return merge(left_sorted, right_sorted)
def merge(left, right):
result = []
while (left and right):
if left[0] < right[0]:
result.append(left[0])
left.pop(0)
else:
result.append(right[0])
right.pop(0)
if left:
result += left
if right:
result += right
return result
```