 edges that start at the same vertex and have
the same label.<p>

This change can be reflected in the language of CCalc by replacing the
proposition

<pre>
shoot causes -alive
</pre>

in the original formalization of the shooting domain with

<pre>
shoot may cause -alive.
</pre>

<tt>may cause</tt> propositions, like <tt>causes</tt> propositions, can be
conditional (that is, followed by <tt>if</tt>...).<p>

<b>Exercise 2.6.</b>
In the modified domain, the assumptions of the Yale Shooting Problem
(the person