Instance Inhabitant_share : Inhabitant share := Share.bot.(* TODO: remove this, it's already in sublist.v *) 
Instance Inhabitant_mpred : Inhabitant mpred := @FF mpred Nveric.

Lemma extract_nth_sepcon : forall l i, 0 <= i < Zlength l -> fold_right sepcon emp l = Znth i l * fold_right sepcon emp (upd_Znth i l emp).