End FilterSubseq.
Arguments subseq_uniqP [T s1 s2].
Section EqMap.
Variables (n0 : nat) (T1 : eqType) (x1 : T1).
Variables (T2 : eqType) (x2 : T2) (f : T1 -> T2).
Implicit Type s : seq T1.

Lemma nth_index_map s x0 x :
{in s &, injective f} -> x \in s -> nth x0 s (index (f x) (map f s)) = x.