Opaque member_dec.

Lemma union_pred_proj: forall m {A} (P: forall it, A it -> val -> mpred) (i: ident) v p d,
members_no_replicate m = true ->
in_members i m ->
(forall i' (v': A (i', field_type i' m)), in_members i' m -> P _ v' p |-- P _ d p) ->
union_pred m P v p |-- P _ (proj_union i m v d) p.