Codual

"For a relation P ⊆ A 2 {\displaystyle P\subseteq A^{2}} , the codual relation is defined as P c d = { ( x , y ) ∈ A 2 ∣ ( y , x ) ∉ P } {\displaystyle P^{\mathit {cd}}=\left\{(x,y)\in A^{2}\mid (y,x)\not \in P\right\}} ."