The transitive reflexive reduction of a partial order. An element 
of a partially ordered set 
covers another element 
provided that there exists no third element 
in the poset for which 
. In this case, 
is called an "upper cover" of 
and 
a "lower cover" of 
.
Cover Relation
See also
Between, Hasse Diagram, Partial OrderExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Cover Relation." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/CoverRelation.html