Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
Walks in bidirected graphs. (a) A valid walk enters and exits a node through opposite edge-orientations. (b) An invalid walk enters and exits a node through identical edge-orientations. (c) Reversing all edge-orientations adjacent to a node results in the same valid and invalid walks
