title: Expressing that a specific subset of X's have property Y in core.logic
body: <p>I want to:</p>
  
  <ol>
  <li>Describe a fact about a subset of a class of objects.</li>
  <li>Declare that an object has a property that consists of other properties.</li>
  </ol>
  
  <p>Take the following as an example:</p>
  
  <pre><code>Red robotic birds are only composed of buttons, cheese, and wire.
  </code></pre>
  
  <p>I want to express that a class of birds, birds that are red and robotic, have a property.
  This property is that they are composed only of buttons, cheese, and wire. There are no restrictions on the type of wire cheese or buttons. Also as a result, it should be deducible that there are no red robotic birds that are composed of paper. Also, these birds can be composed of a subset of the items buttons, cheese, and wire.</p>
  
  <p>In clojure/core.logic.prelude, there are relations and facts using <code>defrel</code> and <code>fact</code>.
  However, I can't come up with a combination to explain this fact. </p>