The digraph:
{'a': ['c'], 'b': ['c'], 'c': ['b', 'd', 'e'], 'd': ['c'], 'e': ['b'], 'f': []}

  Seek path from "a" to "b"
['a', 'c', 'b']

  The nodes:
['a', 'b', 'c', 'd', 'e', 'f']

  The edges:
[['a', 'c'], ['b', 'c'], ['c', 'b'], ['c', 'd'], ['c', 'e'], ['d', 'c'], ['e', 'b']]
  Graphics saved as "digraph.dot.png"

  The isolated nodes:
['f']

  Add node "c":
Node c is already in the digraph.
  Add node "h":
  Updated node list:
['a', 'b', 'c', 'd', 'e', 'f', 'h']

  Add edge "a->f":
  Updated edge list.
[['a', 'c'], ['a', 'f'], ['b', 'c'], ['c', 'b'], ['c', 'd'], ['c', 'e'], ['d', 'c'], ['e', 'b']]

  List all edges from node "c":
[['c', 'b'], ['c', 'd'], ['c', 'e']]

  List all edges to node "c":
[['a', 'c'], ['b', 'c'], ['d', 'c']]