title: Why doesn't ICollection<T> implement ICollection?
body: <p><code>IEnumerable&lt;T&gt;</code> implements <code>IEnumerable</code>.<br>
  But <code>ICollection&lt;T&gt;</code> does not implement <code>ICollection</code>.</p>
  
  <p>What was the rationale for this and/or was it just an oversight?</p>