Antisymmetric

A relation ‘R’ is said to be antisymmetric if xRy and yRx then x=y ∀x,y∈A If (x,y)∈R then (y,x)∈R only if x=y ∀x,y∈A

That means R can contain elements of the form (a,a),(c,d) but must not contain (d,c)