      \fitem{permute}{(t:tab, n:numeric)} returns a new tab which contains the
      \code{n}th permutations of the elements of \code{t}. They are
      factorial \code{s} permutations, where \code{s} is the size of
      \code{t}. The first permutation is numbered 0 and corresponds to the
      permutation which rearranges the elements of \code{t} in an array
      $t_0$ such that they are sorted increasingly. The tab $t_0$ is the
      smallest element amongst all tab that can be done by rearranging the
      element of \code{t}.
      %% 
      The first permutation rearranges the elements of \code{t} in a tab
      $t_1$ such that $t_0 < t_1$ for the lexicographic order and such
      that any other permutation gives an array $t_k$ lexicographicaly
      greater than $t_0$ and $t_1$. Etc. The last permutation (factorial
      \code{s} - 1) returns a tab where all elements of \code{t} are in
      decreasing order.
      \begin{lstlisting}
            $t := [1, 2, 3]
            @permute($t, 0) == [1, 2, 3]
            @permute($t, 1) == [1, 3, 2]
            @permute($t, 2) == [2, 1, 3]
            @permute($t, 3) == [2, 3, 1]
            @permute($t, 4) == [3, 1, 2]
            @permute($t, 5) == [3, 2, 1]
      \end{lstlisting} %$



      %%% -------------------------------------------------------

