title: How do I omit a value in typescript union type
body: <p>I have a type:</p>
  <pre><code>export type Example = ExampleOne | ExampleTwo | ExampleThree;
  </code></pre>
  <p>How do I create a new type <code>ExampleX</code> which only contains <code>ExampleOne</code> or <code>ExampleTwo</code>?</p>
  <p>I tried:</p>
  <pre><code>export type ExampleX = Omit&lt;Example, 'ExampleThree'&gt;;
  </code></pre>
  <p>But that doesn't work?</p>