&quot;, is known as a &quot;stone&quot;.

2.  A bare terminal edge, &quot;|&quot;, is known as a &quot;stick&quot;.

3.  Let the &quot;replacement expression&quot; of the shape &quot;Q[o/x]&quot; mean
    the expression that results from Q by replacing every token
    of the marker &quot;x&quot; with a blank, that is to say, erasing &quot;x&quot;.

4.  Let the &quot;replacement expression&quot; of the shape &quot;Q[|/x]&quot; mean
    the expression that results from Q by replacing every token
    of the ma