Directed Acyclic Graphs

ancestors(G, source)	Return all nodes having a path to in G.
descendants(G, source)	Return all nodes reachable from in G.
topological_sort(G[, nbunch])	Return a list of nodes in topological sort order.
topological_sort_recursive(G[, nbunch])	Return a list of nodes in topological sort order.
is_directed_acyclic_graph(G)	Return True if the graph G is a directed acyclic graph (DAG) or
is_aperiodic(G)	Return True if G is aperiodic.