<ol>
  <li>
   Write a function <code>is_sorted : string array -> bool</code> which
   checks if the values of the input array are sorted in
   strictly increasing order, implying that its elements are unique
   (use <code>String.compare</code>).
  </li>
  <li>
    Using the
    <a href="https://en.wikipedia.org/wiki/Binary_search_algorithm">
      binary search algorithm</a>, an element can be found very
    quickly in a sorted array.
    
    <br/>

    Write a function <code>find : string array -> string