ii. Isolation
 \(d\left(x,y\right)=0\ \Leftrightarrow\ x=y\)
\(1-\frac{\left|X\cap Y\right|}{\left|X\cup Y\right|}=0\)
\(\Rightarrow\frac{\left|X\cap Y\right|}{\left|X\cup Y\right|}=1\)