## Combinations without putting back

Combinations are the number of possible subsets out of a set (note: not ordered; if it were ordered, that would be called Variation).

The number of possible combinations of taking 1 item out of a *set* of N items is N.

The number of possible combinations C of taking n items out of a *set* of N items (when putting them back only after taking all the n items) is:

that is, "all!" divided by "good!"⋅"bad!".

## Properties

(because we are talking of an set, which is unordered)

## Combinations with putting back

TODO