title: How to make IEnumerable<string>.Contains case-insensitive?
body: <p>Suppose I have a .net Array of strings.</p>
  
  <pre><code>string[] strings = new string[] { "AbC", "123", "Xyz", "321" };
  </code></pre>
  
  <p>If I wanted to see if the array of strings contains "ABC", I could write</p>
  
  <pre><code>strings.Contains("ABC");
  </code></pre>
  
  <p>However, suppose that I want a function that will return true if the uppercase values of the strings contain "ABC".  I could uppercase the entire array, but it looks like the <code>.Contains</code> method has some overloads for specifying the comparison, but I'm confused by the syntax.</p>
  
  <p>How can I use the <code>IEnumerable&lt;string&gt;.Contains()</code> method implement this logic?</p>