let notexists_vars frame xs p =
let _,xta = varmem_at frame Here in
List.fold_left
(fun p x ->
let ta0 = F.var xta in
let v_x = D.Xindex.get_ind x in
let q = F.p_eq (D.e_app2 "access" ta0 v_x) (F.e_int 0) in
F.p_implies q p
) p xs