1Note that these are possibilities, not plans nor promises.
2
3- graph periphery: the subgraph of graph center vertices
4- finding the shortest cycle: easy for directed (*), but how about undirected?
5  (*) http://www.cs.auckland.ac.nz/~ute/220ft/graphalg/node14.html
6  do a BFS, when sees an already seen vertex, a cycle of length of at most
7  twice the current depth of the BFS has been found; no cycles => V + 1 (Inf)
8- bipartite aka 2-colourable: again, BFS:
9  http://www.cs.auckland.ac.nz/~ute/220ft/graphalg/node15.html
10- Eulerian circuit: Fleury's algorithm:
11  http://planetmath.org/encyclopedia/FleurysAlgorithm.html
12- could_be_isomorphic() - go second degree?
13
141. separate external and internal attributes?
152. biconn: add next_root
163. DAG SSSP
174. flow: Ford-Fulkerson/Edmonds-Karp/preflow-push?  Floyd-Warshall variant?
18
19-- Classics --
20
21Undirected graphs
22- connectivity
23  - given two vertices are they on a cycle
24  - find_all_paths($u, $v)?
25  - find_all_cycles()? NP-complete; equivalent to finding all Hamiltonians
26- Euler tour
27- bipartite matching: Hopcroft - Kraft
28- 2-colorability (see above)
29- planarity
30
31Digraphs
32- disallow_selfloops => 1?
33- odd-length cycle
34- shortest paths (bfs)
35- squaring a graph: for (u,v)(v,w) add (u,w) unless already there
36
37- graph union, graph difference?
38
39Various specialized graph constructors?
40- n-dim grid (with wraps and connectors -> wheels (webs), cones),
41  circle, star, platonic solids, trees, etc.
42