RankPermutation::usage = "RankPermutation[p] gives the rank of permutation p in lexicographic order."
RankPermutation[{1}] := 0
RankPermutation[{}] := 0
RankPermutation[p_?PermutationQ] :=
        Block[{$RecursionLimit = Infinity},
              (p[[1]]-1) (Length[Rest[p]]!) +
              RankPermutation[ Map[(If[#>p[[1]], #-1, #])&, Rest[p]]]
        ]

UP[r_Integer, n_Integer] :=
        Module[{r1 = r, q = n!},
               Table[r1 = Mod[r1, q];
                     q = q/(n - i + 1);
                     Quotient[r1, q] + 1,
                     {i, n}
               ]
        ]

UnrankPermutation::usage = "UnrankPermutation[r, l] gives the rth permutation in the lexicographic list of permutations of list l. "
UnrankPermutation[r_Integer, {}] := {}
UnrankPermutation[r_Integer, l_List] :=
        Module[{s = l, k, t, p = UP[Mod[r, Length[l]!], Length[l]]},
               Table[k = s[[t = p[[i]] ]];
                     s = Delete[s, t];
                     k,
                     {i, Length[ p ]}
               ]
        ]