e from that
commit, following the commit ancestry chain.</p>
</div>
<div class="paragraph">
<p>To exclude commits reachable from a commit, a prefix <em>^</em>
notation is used.  E.g. <em>^r1 r2</em> means commits reachable
from <em>r2</em> but exclude the ones reachable from <em>r1</em>.</p>
</div>
<div class="paragraph">
<p>This set operation appears so often that there is a shorthand
for it.  When you have two commits <em>r1</em> and <em>r2</em> (named according
to the syntax explained in SPECI