title: How to unmerge a Git merge?
body: <p>I accidentally did a <code>git pull origin master</code> from dev, and master got merged into dev.
  Is it possible to unmerge?</p>
  <p>I've already seen different solutions, i tried this one from both dev and master :
  <code>git revert -m 1 &lt;commit&gt;</code> (once each)
  But i got : Everything is up-to-date, each time</p>