Hi,
(%i2) is_bipartite(empty_graph(0));
Evaluation took 0.0040 seconds (0.0001 elapsed) using 1.148 KB.
(%o294) false
though obviously the graph without vertices is bipartite (2-colourable).
By the way, we also have
(%i3) complete_graph(0);
Argument 1 to complete_graph is not a positive integer
-- an error. To debug this try debugmode(true);
where the K_n, the complete graph with n vertices, is also
well-defined for n = 0.
Oliver