Cover
A set of sets is said to cover another set
if
.
The notion of covering is extremely broad, and mathematicians are often interested in covers where particular restrictions are placed on the . For example, if we have only finitely many of the
(the index set
is finite), we have a finite cover. If
is countable, we have a countable cover. In topology, one may be interested in the case that the
are open sets, in which case we have an open cover.
This article is a stub. Help us out by expanding it.