XNOR similarity

Definition
The similiarity function XNOR is a similarity function $$XNOR: \{0,1\}\times \{0,1\}\longrightarrow [0,1]$$ such that $$\forall x,y\in \{0,1\}$$
 * $$XNOR(x,y)=

\left\{% \begin{array}{ll} 1, & \hbox{si $x=y$;} \\ 0, & \hbox{si $x\neq y$.} \\ \end{array}% \right. $$

Normalization
It is normalized.