title: How does LINQPad reference other classes, e.g. Books in the LINQ in Action samples
body: <p>I'm using LINQPad to create LINQ queries in an application I'm bulding.</p>
  
  <p>I noticed that in the downloaded <strong>LINQ in Action</strong> samples, e.g. example 4.04, intellisense shows a class "Books" but I don't see any <strong>references</strong> or "<strong>using</strong>" statements in the LINQPad tool, here is the sample:</p>
  
  <pre><code>List&lt;Book&gt; books = new List&lt;Book&gt;() {
    new Book { Title="LINQ in Action" },
    new Book { Title="LINQ for Fun" },
    new Book { Title="Extreme LINQ" } };
  
  var titles =
    books
      .Where(book =&gt; book.Title.Contains("Action"))
      .Select(book =&gt; book.Title);
  
  titles.Dump();
  </code></pre>
  
  <p>In "LinqBooks.Common, Business Objects, <strong>Book.linq</strong>" is where the class seems to be defined:</p>
  
  <pre><code>public class Book
  {
    public IEnumerable&lt;Author&gt; Authors {get; set;}
    public String Isbn {get; set;}
    public String Notes {get; set;}
    public Int32 PageCount {get; set;}
    public Decimal Price {get; set;}
    public DateTime PublicationDate {get; set;}
    public Publisher Publisher {get; set;}
    public IEnumerable&lt;Review&gt; Reviews {get; set;}
    public Subject Subject {get; set;}
    public String Summary {get; set;}
    public String Title {get; set;}
    public String Test {get; set;}
  
    public override String ToString()
    {
      return Title;
    }
  }
  </code></pre>
  
  <p><strong>But how does this work so that I can copy in my classes and use LINQPad to quickly build LINQ statements that I can then copy back into my application?</strong></p>