title: git partial pull
body: <p>I am maintaining a repository <strong>A</strong>.</p>
  
  <p>Another contributor has cloned <strong>A</strong> to another repository <strong>B</strong>.</p>
  
  <p>Later, the other contributor added files <em>F</em>, which is irrelevant to me, into <strong>B</strong>.</p>
  
  <p>Now I want to merge changes in <strong>B</strong> back to <strong>A</strong>, but without committing <em>F</em>. How to do so?</p>