Don't add to a list the same value
<p>I have a list of tickets.  Each ticket belongs to a single event.  I want create a list of all events from tickets.  I can get this list, but the same event (value) is repeated in the list. How can I ensure that an event is only added the list once?</p>

<pre><code> List&lt;int&gt; tickets = new List&lt;int&gt;();

 List&lt;Event&gt; events = new List&lt;Event&gt;();

 foreach (var s in tickets)
 {
     events.Add(_context.Event.Find(s));
 }
</code></pre>
