Consider an infinite repository containing balls of 
different types. Then the following table summarizes the number
of distinct ways in which 
balls can be picked for four common definitions of "distinct."
| type of picking | name | symbol name | symbol |
| ordered samples with replacement | string | power |  |
| ordered sample without replacement | permutation |  | |
| unordered samples with replacement | multiset | multichoose |  |
| unordered samples without replacement | combination | binomial coefficient, choose |  |
