title: Using Linq with 2D array, Select not found
body: <p>I want to use Linq to query a 2D array but I get an error:</p>
  
  <blockquote>
    <p>Could not find an implementation of the query pattern for source type 'SimpleGame.ILandscape[<em>,</em>]'.
        'Select' not found.  Are you missing a reference to 'System.Core.dll' or a using directive for 'System.Linq'?</p>
  </blockquote>
  
  <p>Code is following:</p>
  
  <pre><code>var doors = from landscape in this.map select landscape;
  </code></pre>
  
  <p>I've checked that I included the reference <code>System.Core</code> and using <code>System.Linq</code>.</p>
  
  <p>Could anyone give some possible causes?</p>