Definition inj_on_list {A B} (l : list A) (f : A -> B) :=
forall x y, In x l -> In y l -> f x = f y -> x = y.
Definition subset_rel {X} (sub lst : list X) : Prop :=
forall x,
In x sub ->
In x lst.
(*** NoDup general lemmas ***)

(* TODO: make generic and move elsewhere *)
Lemma NoDup_remove_list_sub : forall (dlt lst : list block),
NoDup (List.map block_blockid lst) ->
NoDup (List.map block_blockid (remove_list_sub eqb dlt lst)).