title: Could I use operator == if I only implemented operator <?
body: <p>I have implemented <code>operator&lt;</code> for a certain object.
  Logically, if <code>!(a &lt; b)</code> and <code>!(b &lt; a)</code> it means <code>a == b</code>.</p>
  
  <p>Is this inferred automatically? Can I use <code>==</code> if I only implement <code>&lt;</code>?</p>