End SortKeys.
End SortKeys.
Hint Resolve SortKeys.perm.
Hint Resolve SortKeys.uniq.
Hint Resolve SortKeys.E.
Notation sort_keys      := SortKeys.f.
Notation sort_keys_perm := SortKeys.perm.
Notation sort_keys_uniq := SortKeys.uniq.
Notation sort_keysE     := SortKeys.E.
Notation eq_sort_keys   := SortKeys.eq.
Section ChoiceKeys.
Variable (K : choiceType).
Implicit Types (k : K) (ks : seq K).

Lemma mem_sort_keys ks k : k \in ks -> k \in sort_keys ks.