PROBLEM 2: Consider a finite set S with n elements; the number of distinct subsets of S with exactly two is called "n choose 2" and typically written as ). You may Recall that C)=mi. Below is a (trivial) C++function which takes a non-negative integer n and returns () (also a non-negative integer): unsigned int n_choose_2(unsigned int n) if (n--e) return 0; else return n* (n-1)/2; Your job: write a function which also returns () but with the following constraints: You cannot use the multiplication operator , You cannot use the division operator , . You cannot have any loops . You cannot add any additional parameters to the function . Your function must be self-contained: no helper functions! . You cannot use any globals . You cannot use any static variables . You cannot use any"bit twiddling" operations no shifts, etc. However, ..- e You can use recursion You can use the 4, and -' operators. You will submit a scanned hardcopy (hand-written or printed) or pdf via gradescope. Of course, you are free to try out your solution in a real program. In addition: argument of correctness required! You must explain the logic of your solution! In other words, explain why it works. Think in terms of an inductive argument. Just giving a correct C+ function is not sufficient and will not receive many points (possibly zero!) Another note: an example is not an argument of correctness