21.2: Definition
( \newcommand{\kernel}{\mathrm{null}\,}\)
We often want to count how many ways we can “mix up” the objects in a collection.
a bijection from a finite set to itself
Once you have written the elements of a finite set in some order, think of a permutation as a way of re-ordering them.
Figure \PageIndex{1} contains tables of values for all six possible permutations of the set A = \{a,b,c\}\text{.} We have grouped them according to: all elements fixed; one element fixed and two mixed; all elements mixed.
