title: How do I tell if the input has used duplicate letters?
body: <pre><code>list = [ &quot;A&quot;, &quot;B&quot; ,&quot;C&quot;,&quot;T&quot;]
  </code></pre>
  <p>I want to make a word from letters in a string. If the user inputs &quot;cat&quot; then that's correct, but if it's &quot;CATT&quot; then that's wrong. How would I detect that? The computer just sees if &quot;A,B,C,T&quot; is used but not how many times.</p>