1. Show that, during an add (x) or a remove(x) operation, the expected number of pointers in a SkiplistSet that get changed is constant.
2. Design and implement a version of a skiplist that implements the SSet interface, but also allows fast access to elements by rank. That is, it also supports the function get (i), which returns the element whose rank is i in O(log n) expected time. (The rank of an element x in an SSet is the number of elements in the SSet that are less than x.)