A relation 
on a set 
is irreflexive provided that no element is related to itself;
in other words, 
for no 
in 
.
Irreflexive
See also
RelationExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Irreflexive." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Irreflexive.html