title: How to determine if one array contains all elements of another array
body: <p>Given:</p>
  
  <pre><code>a1 = [5, 1, 6, 14, 2, 8]
  </code></pre>
  
  <p>I would like to determine if it contains all elements of:</p>
  
  <pre><code>a2 = [2, 6, 15]
  </code></pre>
  
  <p>In this case the result is <code>false</code>.</p>
  
  <p>Are there any built-in Ruby/Rails methods to identify such array inclusion?</p>
  
  <p>One way to implement this is:</p>
  
  <pre><code>a2.index{ |x| !a1.include?(x) }.nil?
  </code></pre>
  
  <p>Is there a better, more readable, way?</p>