Git: cancel an interactive rebase

You can make vim exit with a non-zero exit code to cancel the rebase by typing :cq. The result of this is:

$ git rebase -i HEAD~4
# enter vim, then type :cq<enter>
Could not execute editor

From the vim help page we see that cq is short for cquit:

                                                        *:cq* *:cquit*
:cq[uit][!]             Quit Vim with an error code, so that the compiler
                        will not compile the same file again.
                        WARNING: All changes in files are lost!  Also when the
                        [!] is not used.  It works like ":qall!" |:qall|,
                        except that Vim returns a non-zero exit code.