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.
In the strict approach, mutation involving breaking any ring is not allowed (red arrows). Here, “ring breaking” refers to any transformation where atoms remaining in the final system were part of any ring which has been removed. In the loose approach, ring breaking mutations are allowed only when the ring system left behind is rigid (green arrows).
