$b\in\left\{b,\ g,\ 5,\ 8,\ 12\ \right\}$  

 $x\notin\left\{b,\ g,\ 5,\ 8,\ 12\right\}$  

 $3\in\left\{b,\ g,\ 5,\ 8,\ 12\right\}$  

 $6\notin\left\{b,\ g,\ 5,\ 8,\ 12\right\}$  

{x | x is an even number between 3 and 5}

$\left\{x\in\mathbb{Z}\ :\ x^2=5\right\}$

$\left\{x\ \in\mathbb{Z}:\ x=0\ \vee\ x=-5\right\}$

{x | x is a natural number divisible by 2}

 $C=\left\{x\in\mathbb{Z}\ :\ x^2\le9\right\}$  

 $C=\left\{x\in\mathbb{Z}\ :\ x\le3\right\}$  

 $C=\left\{x\in\mathbb{Z}:\ -3<x<3\ \right\}$  

 $C=\left\{x\in\mathbb{Z}\ :\ x+1=3\right\}$