Definition list_disjoint {A: Type} (l1 l2: list A) : Prop :=   (* THIS IS FROM compcert/Coqlib.v *)
forall (x y: A), In x l1 -> In y l2 -> x <> y.
Inductive pshareval_join' {A}{JA: Join A}
: option (pshare * A) ->  option (pshare * A) ->  option (pshare * A) -> Prop :=
| pshareval_None1: forall x, pshareval_join' None x x
| pshareval_None2: forall x, pshareval_join' x None x
| pshareval_Some: forall x y z,
join (fst x) (fst y) (fst z) ->
join (snd x) (snd y) (snd z) ->
pshareval_join' (Some x) (Some y) (Some z).

Lemma pshareval_join_i{A}{JA: Join A}: forall a b c, pshareval_join' a b c -> join a b c.
Module Type ENV.