SimpleArc<V> 
A simple arc has two vertices: head and tail.

SimpleEdge<V> 
A simple edge has two vertices.

SparseDAGraph<V,E extends Arc<V>> 
This class implements the sparse directed acyclic graph representation.

SparseDiGraph<V,E extends Arc<V>> 
This class implements the sparse directed graph representation.

SparseGraph<V,E extends HyperEdge<V>> 
This class implements the sparse graph representation.

SparseTree<V> 
This class implements the sparse tree representation.

SparseUnDiGraph<V,E extends UndirectedEdge<V>> 
This class implements the sparse undirected graph representation.

VertexTree<T> 
A VertexTree is both a tree and a vertex/node.This implementation builds a tree
incrementally and recursively (combining trees).
