Re: symmetric difference with --left-only vs. range notation

"D. Ben Knoble" [off-list ref] writes:

    git rev-list --count --left-only @{u}...
    git rev-list --count ..@{u}

In my estimation, since we're not using --cherry-pick here, the first
says "list (count) the commits on upstream but not in HEAD, since the
merge-base (which is reachable from both)" while the second says "list
(count) the commits on upstream but not in HEAD." Is there ever a
situation where those sets aren't the same?

I don't think of any; let us know when you find a case that the
above does not hold true ;-).