Merge sort, the recursion part

Question

After studying the merge sort for a couple of days, I understand it conceptually, but there is one thing that I don\'t get.

What I get:

1.) It takes a list, for

Answer 1

Once the list only contains one element, each pair of leaves are sorted and joined. Then you can traverse through the list and find out where the next pair should be inserted. The recursion "knows" nothing about going back up the recursion tree, rather it is the act of sorting and joining that has this effect.