
  useful interval type, the numbers should respect some requirements. Please
  refer to <a href="numbers.htm">this page</a> in order to see them. When
  your base type is robust enough, you can go to the next step: the choice of
  the policies.</p>

  <p>As you should already know if you did not come to this page by accident,
  the <code>interval</code> class expect a policies argument describing the
  <a href="rounding.htm">rounding</a> and <a href="checking.htm">checking</a>
  policies. The first thing t