For Mozart-Oz Programming. Can you also explain this to me

Suppose that you are given an arithmetic expression described by a tree constructed from tuples as follows: 1. An integer is described by a tuple int(N), where N is an integer. An addition is described by a tuple add(X Y), where both X and Y are arithmetic expressions A multiplication is described by a tuple mul(X Y), where both X and Y are arithmetic expressions 1. 2. 3. Implement a function Eval that takes an arithmetic expression and returns its value. For example, add(int(1) mul(int(3) int(4)) is an arithmetic expression and its evaluation returns 13