tabase</a>, and updating the remote
head ref. If the remote <a href="#def_head">head</a> is not an
ancestor to the local head, the push fails.</p>
</dd>
<dt class="hdlist1"><a id="def_reachable"></a>reachable</dt>
<dd>
<p>All of the ancestors of a given <a href="#def_commit">commit</a> are said to be
"reachable" from that commit. More
generally, one <a href="#def_object">object</a> is reachable from
another if we can reach the one from the other by a <a href="#def_chain">chain</a>
that follows <a href="#def