The primary data structures of HugoLib are the graph classes. They all

 provide a node list - edge list interface, i.e. they have

 functionalities to list the nodes and the edges of the graph as well

 as in incoming and outgoing edges of a given node. 

 Each graph should meet the \ref ConstGraph concept. This concept does

 makes it possible to change the graph (i.e. it is not possible to add

 or delete edges or nodes). Most of the graph algorithms will run on

 these graphs.

 The graphs meeting the \ref ExtendableGraph concept allow node and

 edge addition. You can also "clear" (i.e. erase all edges and nodes)

 such a graph.

 In case of graphs meeting the full feature \ref ErasableGraph concept

 you can also erase individual edges and node in arbitrary order.

 The implemented graph structures are the following.

 \li \ref hugo::ListGraph "ListGraph" is the most versatile graph class. It meets

 the ErasableGraph concept and it also have some convenience features.

 \li \ref hugo::SmartGraph "SmartGraph" is a more memory

 efficient version of \ref hugo::ListGraph "ListGraph". The

 price of it is that it only meets the \ref ExtendableGraph concept,

 so you cannot delete individual edges or nodes.

 \li \ref hugo::SymListGraph "SymListGraph" and

 \ref hugo::SymSmartGraph "SymSmartGraph" classes are very similar to

 \ref hugo::ListGraph "ListGraph" and \ref hugo::SmartGraph "SmartGraph".

 The difference is that whenever you add a

 new edge to the graph, it actually adds a pair of oppositely directed edges.

 They are linked together so it is possible to access the counterpart of an

 edge. An even more important feature is that using these classes you can also

 attach data to the edges in such a way that the stored data

 are shared by the edge pairs. 

 \li \ref hugo::FullGraph "FullGraph"

 implements a full graph. It is a \ref ConstGraph, so you cannot

 change the number of nodes once it is constructed. It is extremely memory

 efficient: it uses constant amount of memory independently from the number of

 the nodes of the graph. Of course, the size of the \ref maps "NodeMap"'s and

 \ref maps "EdgeMap"'s will depend on the number of nodes.

 \li \ref hugo::NodeSet "NodeSet" implements a graph with no edges. This class

 can be used as a base class of \ref hugo::EdgeSet "EdgeSet".

 \li \ref hugo::EdgeSet "EdgeSet" can be used to create a new graph on

 the edge set of another graph. The base graph can be an arbitrary graph and it

 is possible to attach several \ref hugo::EdgeSet "EdgeSet"'s to a base graph.

 \todo Don't we need SmartNodeSet and SmartEdgeSet?

 \todo Some cross-refs are wrong.

 The graph structures itself can not store data attached

 to the edges and nodes. However they all provide

 \ref maps "map classes"

 to dynamically attach data the to graph components.