t a simplified implementation of the
<TT>random_access_iterator_property_map</TT> class
which we will name <TT>iterator_pa</TT>.

<P>
We start with the definition of the <TT>iterator_map</TT> class
itself. This adaptor class is templated on the adapted <TT>Iterator</TT>
type and the ID property map. The job of the ID property map
is to map the key object (which will typically be a vertex or edge
descriptor) to an integer offset. The <TT>iterator_map</TT> class will
need the three necessary typedefs for a pr