Definition[]
Given a universe set 
, the identity similarity function is a function 
defined as
Failed to parse (unknown function "\begin{array}"): {\displaystyle IdSim(x,y)= \left\{% \begin{array}{ll} 1, & \hbox{if $x=y$;} \\ 0, & \hbox{if $x\neq y$.} \\ \end{array}% \right. }
This similarity could be applied to every set but give no information about the grade of resemblance between 
and 
when they are different.
Examples[]
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