When you merge two sorted lists, you only have to compare the first element of each, since you can trust that all of the other elements are bigger. All the steps before that are there to make sure that is true.
It doesn’t matter. You check the first of each group and pick the smallest, then compare the one you didn’t pick with the next one of the other group. In your example, you would pick all of the ones from the right side and once it is empty, just add all the ones on the left.
When you merge two sorted lists, you only have to compare the first element of each, since you can trust that all of the other elements are bigger. All the steps before that are there to make sure that is true.
Wait, how do I know that all four of the right half aren’t smaller than all four of the Left half?
It doesn’t matter. You check the first of each group and pick the smallest, then compare the one you didn’t pick with the next one of the other group. In your example, you would pick all of the ones from the right side and once it is empty, just add all the ones on the left.
You don’t, and they can be.
Watch the animation on Wikipedia: https://en.wikipedia.org/wiki/Merge_sort