Permutations
A permutation of a set of distinct objects is an ordered arrangement of
(a,b,c) (a,c,b) (b,a,c) (b,c,a) (c,a,b) (c,b,a)
An ordered arrangement of r elements of a set is called an
1-permutations of {a,b,c}:
2-permutations of {a,b,c}:
(a,b) (a,c) (b,a) (b,c) (c,a) (c,b)
3-permutations of {a,b,c} --- the same as permutations of {a,b,c}.