Question 142803

The elements of a set can be listed out according to a rule, such as:
{{{x}}} is a natural number,{{{ x < 5}}}

If you're going to be technical, you can use full "set-builder notation", which looks like this:

{x| x is element of N, x<5}

This is pronounced as "the set of {{{all}}}{{{ x}}}, such that {{{x }}}is an element of the natural numbers and {{{x }}}is less than {{{5}}}". 

The vertical bar is usually pronounced as "such that", and it comes between the name of the variable you're using to stand for the elements and the rule that tells you what those elements actually are. This same set, since the elements are few, can also be given by a listing of the elements, like this:
{1, 2, 3, 4, 5}