title: fatal: Needed a single revision
body: <p>My repo has 3 commits. I want to squash to one.</p>
  
  <p>I ran <code>git rebase -i HEAD~3</code> and got this error:</p>
  
  <pre><code>fatal: Needed a single revision
  invalid upstream HEAD~3
  </code></pre>
  
  <p>I was able to run <code>git rebase -i HEAD~2</code> and then <code>git push origin +master</code> and now I have 2 commits.</p>
  
  <p>But why couldn't I do <code>git rebase -i HEAD~3</code>?</p>