Opaque member_dec.

Lemma struct_pred_ext_derives: forall m {A0 A1} (P0: forall it, A0 it -> val -> mpred) (P1: forall it, A1 it -> val -> mpred) v0 v1 p,
members_no_replicate m = true ->
(forall i d0 d1, in_members i m ->
P0 _ (proj_struct i m v0 d0) p |-- P1 _ (proj_struct i m v1 d1) p) ->
struct_pred m P0 v0 p |-- struct_pred m P1 v1 p.