cencyGraph concept provides an interface for efficient access
of the adjacent vertices to a vertex in a graph. This is quite similar
to the <a href="./IncidenceGraph.html">IncidenceGraph</a> concept (the
target of an out-edge is an adjacent vertex). Both concepts are
provided because in some contexts there is only concern for the
vertices, whereas in other contexts the edges are also important.

<H3>Refinement of</H3>

<a href="Graph.html">Graph</a>

<h3>Notation</h3>

<Table>
<TR>
<TD><tt>G</tt></TD>
<TD>A