title: Can I define a generic type constraint on DU Keys?
body: <p>Is there a way to define a generic type constraint such that</p>
  <pre><code>//this will compile
  type Contrained = StrongConstraint&lt;&quot;a&quot; | &quot;b&quot; | &quot;c&quot;, &quot;a&quot; | &quot;b&quot;&gt;
  
  //this wont compile as &quot;a&quot; | &quot;b&quot; | &quot;d&quot; is not a strict subset of &quot;a&quot; | &quot;b&quot; | &quot;c&quot;
  type Contrained = StrongConstraint&lt;&quot;a&quot; | &quot;b&quot; | &quot;c&quot;, &quot;a&quot; | &quot;b&quot; | &quot;d&quot;&gt;
  </code></pre>
  <p>This is similar to <code>Exclude</code> just stronger as I dont like keys in the second param that are not part of the first.</p>