Take the 2-minute tour ×  I merged the beta branch into the
master branch. I pushed to origin. I now want master to be as it
was prior to the merger both locally and remotely.  A good
answer for undoing a merge that was already pushed suggests  git
revert -m 1 commit_hash  If this is indeed the way to go, how
can I determine commit_hash? I unsuccessfully tried the hash
returned by merge-base:  $ git merge-base --all master beta $
git revert -m 1 1f4b949b7ef97abf913ae672e3acd0907abfac1b error:
Mainline was specified but commit
1f4b949b7ef97abf913ae672e3acd0907abfac1b is not a merge. fatal:
revert failed  I've examined both git-log and gitk renditions of
the branches, but they're very long, and I am uncertain enough
of my interpretation to feel I should seek assistance before
making a perhaps bigger mess. Beta was derived from v2 which was
derived from master. There have been some mergers from master
into v2 and beta along the way as I've kept the new branches up-
to-date with master. The merger in the direction