///The newly added nodes and edges can be removed using the

     ///The newly added nodes and edges can be removed using the

     ///restore() function.

     ///restore() function.

     ///

     ///

     ///\warning Edge and node deletions cannot be restored.

     ///\warning Edge and node deletions cannot be restored.

     ///\warning SnapShots cannot be nested.

     ///\warning SnapShots cannot be nested.

     ///\todo \c SnapShot or \c Snapshot?

     ///\todo \c SnapShot or \c Snapshot?

     class SnapShot : protected AlterationNotifier<Node>::ObserverBase,

     class SnapShot : protected AlterationNotifier<Node>::ObserverBase,

 		     protected AlterationNotifier<Edge>::ObserverBase

 		     protected AlterationNotifier<Edge>::ObserverBase

     {

     {

       protected:

       protected: