1) Split the list into many smaller lists, recursively, before reconstructing them, during which it sorts the items as needed
2)
+-------+-----+--------+
| Start | End | Middle |
+-------+-----+--------+
|   0   |  8  |    4   |
|   0   |  4  |    2   |
|   0   |  2  |    1   |
+-------+-----+--------+
|   2   |  4  |    3   |
|   4   |  8  |    6   |
+-------+-----+--------+
|   4   |  6  |    5   |
|   6   |  8  |    7   |
+-------+-----+--------+
3) See colliert_merge_question_3.png, colliert_merge_question_3.txt
4)
MergeSort(CU, U, 0, 8)
┣━MergeSort(U, CU, 0, 4)
┃ ┣━━MergeSort(CU, U, 0, 2)
┃ ┣━━MergeSort(CU, U, 2, 4)
┃ ┗━━Merge(U, CU, 0, 2, 4)
┣━MergeSort(U, CU, 4, 8)
┃ ┣━━MergeSort(CU, U, 4, 6)
┃ ┣━━MergeSort(CU, U, 6, 8)
┃ ┗━━Merge(U, CU, 4, 6, 8)
┗━Merge(CU, U, 0, 4, 8)