title: HG: Undo a commit from history
body: <p>I have a HG repository with revs 1, 2, 3, 4, 5 and 6. </p>
  
  <p>When I committed rev 4, I unknowingly botched some changes in rev3 that I should not have. I did not notice this until rev 6 was already committed. </p>
  
  <p>I need to undo changes in rev 4, but then re-apply all other changes after that. Basically undoing commit #4. How can I do that?</p>