title: How git-merge and git-rebase behave with a topic branch forked off of another topic branch?
body: <p>Let us suppose the repository looks like this:</p>
  
  <pre><code>            master
                 |
  A--B--C--K--L--M
         \
          E-F-G
              |\
              | H-I-J
            topicA  |
                  topicB
  </code></pre>
  
  <p>What would <code>git merge topicB</code> do when in <code>master</code>? Would it apply commits <code>H</code>, <code>I</code>, and <code>J</code> only? or all the commits from the initial fork point of <code>topicA</code>?</p>
  
  <p>What would <code>git rebase master topicA</code> do? Would it lead to this:</p>
  
  <pre><code>            master
                 |
  A--B--C--K--L--M
                  \
                   E'-F'-G'
                         |\
                         | H'-I'-J'
                       topicA    |
                               topicB
  </code></pre>
  
  <p>or something more like this?</p>
  
  <pre><code>            master
                 |
  A--B--C--K--L--M
         \        \
          \        E'-F'-G'
           \             |
            \          topicA
             \          
              E-F-G-H-I-J
                        |
                      topicB
  </code></pre>