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.
Flipping a strong triangle using auxiliary edges. The sequence of same-sign edge switches and triangle flips that flips a strong triangle: (1) Opening, (2) Flipping, (3) Closing, and (4) Restoring. Solid lines indicate positive edges and dotted lines indicate negative edges.
