title: My sed code worked... but I have no idea why. Can someone help me understand?
body: <p>I am trying to delete in a file, lines that does not contain two separate terms. I got it to work, but not sure how it worked. </p>
  
  <pre><code>sed -i '/^HETATM/!{/^ATOM/!d}' file
  </code></pre>
  
  <p>can someone explain? </p>