If all named commits are already ancestors of `HEAD`, 'git merge'
will exit early with the message "Already up-to-date."
+Often the current branch head is an ancestor of the named commit.
+This is the most common case especially when invoked from 'git
+pull': you are tracking an upstream repository, you have committed
+no local changes, and now you want to update to a newer upstream
+revision. In this case, a new commit is not needed to store the
+combined history; instead, the `HEAD` (along with the index) is
+updated to point at the named commit, without creating an extra
+This behavior can be suppressed with the `--no-ff` option.
A merge is always between the current `HEAD` and one or more
commits (usually a branch head or tag).
-Two kinds of merge can happen:
-* `HEAD` is already contained in the merged commit. This is the
- most common case especially when invoked from 'git pull':
- you are tracking an upstream repository, have committed no local
- changes and now you want to update to a newer upstream revision.
- Your `HEAD` (and the index) is updated to point at the merged
- commit, without creating an extra merge commit. This is
-* Both the merged commit and `HEAD` are independent and must be
- tied together by a merge commit that has both of them as its parents.
- The rest of this section describes this "True merge" case.
+Except in a fast-forward merge (see above), the branches to be
+merged must be tied together by a merge commit that has both of them
+The rest of this section describes this "True merge" case.
The chosen merge strategy merges the two commits into a single