How to write sets in rule method or set builder form

The general form of a set-builder notation is given as:
{ x : Characteristic of x } or { x | Characteristic of x }
Here, an element of a set is denoted by the letter x (though some other letter can also be used, i.e. y, z, a, b, c etc) which follows a colon symbol (":") or a vertical line ("|").