title: Dictionary search with Linq
body: <p>we can search dictionary like</p>
  
  <pre><code>var dictionary = new Dictionary&lt;string,string&gt;();
  dictionary.Keys.Where( key =&gt; key.Contains("a")).ToList();
  </code></pre>
  
  <p>but it return list. i want that linq should return  true or false. so what would be the right code that search dictionary with linq. please guide.</p>