`git reset --hard <upstream>` (or <newbase>).
The commits that were previously saved into the temporary area are
-then reapplied to the current branch, one by one, in order.
+then reapplied to the current branch, one by one, in order. Note that
+any commits in HEAD which introduce the same textual changes as a commit
+in HEAD..<upstream> are omitted (i.e., a patch already accepted upstream
+with a different commit message or timestamp will be skipped).
It is possible that a merge failure will prevent this process from being
completely automatic. You will have to resolve any such merge failure
The latter form is just a short-hand of `git checkout topic`
followed by `git rebase master`.
+If the upstream branch already contains a change you have made (e.g.,
+because you mailed a patch which was applied upstream), then that commit
+will be skipped. For example, running `git-rebase master` on the
+following history (in which A' and A introduce the same set of changes,
+but have different committer information):
+
+------------
+ A---B---C topic
+ /
+ D---E---A'---F master
+------------
+
+will result in:
+
+------------
+ B'---C' topic
+ /
+ D---E---A'---F master
+------------
+
Here is how you would transplant a topic branch based on one
branch to another, to pretend that you forked the topic branch
from the latter branch, using `rebase --onto`.