title: Linq error: "string[] does not contain a definition for 'Except'."
body: <p>Here's my code:</p>
  
  <pre><code>    public static string[] SplitKeepSeparators(this string source, char[] keptSeparators, char[] disposableSeparators = null)
      {
          if (disposableSeparators == null)
          {
              disposableSeparators = new char[] { };
          }
  
          string separatorsString = string.Join("", keptSeparators.Concat(disposableSeparators));
          string[] substrings = Regex.Split(source, @"(?&lt;=[" + separatorsString + "])");
  
          return substrings.Except(disposableSeparators); // error here
      }
  </code></pre>
  
  <p>I get the compile time error <code>string[] does not contain a definition for 'Except' and the best extension method overload ... has some invalid arguments</code>.</p>
  
  <p>I have included <code>using System.Linq</code> in the top of the source file.</p>
  
  <p>What is wrong?</p>