A possible way of working with permutations is by relating them to the reorderings of the elements of a list. This is the standard point of view in the combinatorial approach ...
When you make a sequence of definitions in Mathematica, some may be more general than others. Mathematica follows the principle of trying to put more general definitions ...
Sort
(Built-in Mathematica Symbol) Sort[list] sorts the elements of list into canonical order. Sort[list, p] sorts using the ordering function p.
RandomSample[{e_1, e_2, ...}, n] gives a pseudorandom sample of n of the e_i.RandomSample[{w_1, w_2, ...} -> {e_1, e_2, ...}, n] gives a pseudorandom sample of n of the e_i ...
AlgebraicNumberDenominator[a] gives the smallest positive integer n such that n a is an algebraic integer.
ImageDifference[image_1, image_2] gives an image in which each pixel is the absolute difference of the corresponding pixels in image_1 and image_2.
SynchronousUpdating is an option for Manipulate, Dynamic, and related functions that specifies whether or not to evaluate their contents synchronously.
TraceOff is an option for Trace and related functions which specifies forms inside which tracing should be switched off.
ViewVertical is an option for Graphics3D and related functions which specifies what direction in scaled coordinates should be vertical in the final image.
$MaxNumber gives the maximum arbitrary-precision number that can be represented on a particular computer system.