summary: Correct length notation

Vector length is customarily denoted by |V|.

* src/current/include/calc-display.xsl (c:sum, c:length-of): Use new
  notation.
* src/current/summary.xsl: Update N.B. with new notation.

src/current/include/calc-display.xsl

@@ -166,9 +166,9 @@
   <xsl:if test="./c:*">
     <!-- the upper limit of the summation will be denoted by #S, where S is the
          symbol for a given set -->
-    <xsl:text>^{\grave\#</xsl:text>
+    <xsl:text>^{|</xsl:text>
       <xsl:copy-of select="$symbol" />
-    <xsl:text>}</xsl:text>
+    <xsl:text>|-1}</xsl:text>
   </xsl:if>
 
   <!-- if no children are provided, just sum @of -->
@@ -695,9 +695,9 @@
 
 
 <xsl:template match="c:length-of">
-  <xsl:text>\#\left(</xsl:text>
+  <xsl:text>|\left(</xsl:text>
     <xsl:apply-templates select="./c:*[1]" />
-  <xsl:text>\right)</xsl:text>
+  <xsl:text>\right)|</xsl:text>
 </xsl:template>
 
 <xsl:template match="c:cons">

src/current/summary.xsl

@@ -2113,7 +2113,7 @@
 
       <dt>Counting Vectors</dt>
       <dd>
-        Let \(\#V\) = the number of values within the vector \(V\); this notation is
+        Let \(|V|\) = the number of values within the vector \(V\); this notation is
         used within certain summations. You may also see the following notations:
 
         <ul>
@@ -2123,7 +2123,7 @@
             count the number of swimming pools).
           </li>
           <li>
-            \(\sum_{k=0}^{\#V-1} 1\) to count the number of values in vector \(V\).
+            \(\sum_{k=0}^{|V|-1} 1\) to count the number of values in vector \(V\).
           </li>
         </ul>
       </dd>