intuition.
eapply listReplace_getSomes_Permutation_h; eauto.
Qed.

Lemma nth_listReplace_ne :
forall (i1 i2 : nat)(A : Set)(ls : list A)(a def : A),
i1 <> i2 ->
nth i1 (listReplace ls i2 a def) def =
nth i1 ls def.