a basic skeleton for a Visitor following the connected components (CC) of a graph
note: you basically need to implement your own enter(), exit() and visit(Vertex v) methods
enter() is called when entering a new CC
exit() is called when finishing the current CC
visit(v) is called when adding v into the current CC
in addition you may override the accept(Edge edge) method to select
proper edges (by default all existing edges are acceptable)
A basic skeleton for compressors with default implementations.
You mostly have to implement the two methods: subsume(v, u) : tells if v S u restore(u) : restore the compressed vertex u to its initial state