<Chapter Label="Operators"><Heading>Operators</Heading>

  <Section><Heading>Operators for digraphs</Heading>
    <List>
     <Mark><C><A>digraph1</A> = <A>digraph2</A></C></Mark>
     <Item>
       <Index Key="="><C>=</C> (for digraphs)</Index>
       returns <K>true</K> if <A>digraph1</A> and <A>digraph2</A> have the same
       vertices, and <C>DigraphEdges(<A>digraph1</A>) =
         DigraphEdges(<A>digraph2</A>)</C>, up to some re-ordering of the edge
       lists. <P/>

       Note that this operator does not compare the vertex labels 
       of <A>digraph1</A> and <A>digraph2</A>.
     </Item>

     <Mark><C><A>digraph1</A> &lt; <A>digraph2</A></C></Mark>
     <Item>
       <Index Key="&lt;"><C>&lt;</C> (for digraphs)</Index>

       This operator returns <K>true</K> if one of the following holds:

       <List>
         <Item>
           The number <M>n_1</M> of vertices in <A>digraph1</A> is less than
           the number <M>n_2</M> of vertices in <A>digraph2</A>;
         </Item>
         <Item>
           <M>n_1 = n_2</M>, and the number <M>m_1</M> of edges in
           <A>digraph1</A> is less than the number <M>m_2</M> of edges in
           <A>digraph2</A>;
         </Item>
         <Item>
           <M>n_1 = n_2</M>, <M>m_1 = m_2</M>, and
           <C>DigraphEdges(<A>digraph1</A>)</C> is less than
           <C>DigraphEdges(<A>digraph2</A>)</C> after having both of these sets
           have been sorted with respect to the lexicographical order.
         </Item>
       </List>
     </Item>
   </List>
  </Section>
</Chapter>
