Function: _header_combinatorics
Class: header
Section: combinatorics
Doc:
 \section{Combinatorics}\label{se:combinat}

 Permutations are represented in gp as \typ{VECSMALL}s and can be input
 directly as \kbd{Vecsmall([1,3,2,4])} or obtained from the iterator
 \kbd{forperm}:
 \bprog
 ? forperm(3, p, print(p))  \\ iterate through S_3
 Vecsmall([1, 2, 3])
 Vecsmall([1, 3, 2])
 Vecsmall([2, 1, 3])
 Vecsmall([2, 3, 1])
 Vecsmall([3, 1, 2])
 Vecsmall([3, 2, 1])
 @eprog

 Permutations can be multiplied via \kbd{*}, raised to some power using
 \kbd{\pow}, inverted using \kbd{\pow(-1)}, conjugated as
 \kbd{p * q * p\pow(-1)}. Their order and signature are available via
 \kbd{permorder} and \kbd{permsign}.
