<p>
  The idea of this exercise is to use the principle of the <code>map</code>
  function to implement algorithms that transform data structures using
  higher-order functions. 
</p>

<ol>
  <li>
    Using the function <code>map</code> from the module <code>List</code>, write
    a function <code>wrap : 'a list -> 'a list list</code> that transforms a
    <code>list</code> of elements <code>'a</code>into a list of singleton lists.

    <br />

    For instance, <code>wrap [1;2;3]</code> is equal to
    <co