Let 
and 
be sets, and let 
be a relation on 
.
Then 
is a concurrent relation if and only if for any finite subset 
of 
, there exists a single element 
of 
such that if 
, then 
. Examples of concurrent relations include the following:
1. The relation 
on either the natural numbers, the integers, the rational numbers, or the real numbers.
2. The relation 
between elements of an extension 
of a field 
, defined by
 |
3. The containment relation 
between open neighborhoods of a given point 
of a topological space 
.
