(* SEPARATION ALGEBRAS *)
(* We use the Section to hide these instances, because  variables-as-resources clients will want Join_env, but global-variables users will want Join_equiv. Only the variables-as-resources clients should add these instances, which is done in the Module EnvSA,  below *)
Parameter Perm_env: forall {PA: Perm_alg A}, Perm_alg (env key A).  Existing Instance Perm_env.
Instance Sep_env {SA: Sep_alg A}: Sep_alg (env key A).
refine (mkSep Join_env (fun _ => empty_env) _ _).
repeat intro; rewrite env_get_empty; constructor.
auto.
Defined.
Instance Sing_env  {SA: Sep_alg A} : Sing_alg (env key A).
refine (mkSing empty_env _). reflexivity.
Defined.
Parameter Canc_env: forall {PA: Perm_alg A}{CA: Canc_alg A}, Canc_alg (env key A). Existing Instance Canc_env.
Parameter Disj_env: forall {PA: Perm_alg A}{DA: Disj_alg A}, Disj_alg (env key A).   Existing Instance Disj_env.
Parameter Cross_env : Cross_alg (env key A).  Existing Instance Cross_env.
(* env_mapsto and the lemmas about it are in a Separation Logic, not just a separation algebra. We have two style of separation logic (direct and ageable), and this module Env is usable with either kind.  Thus, we build primitives whose names start with _ to avoid polluting the namespace; then we reveal them at appropriate types in EnvSL and EnvASL, below. *)
(* ENV_MAPSTO *)
Parameter _env_mapsto: forall {KE: EqDec key}  (id: key) (sh: Share.t) (v: A), pred (env key A).

Axiom _env_mapsto_splittable: forall {KE: EqDec key}  id v (sh sh1 sh2: pshare) rho,
join sh1 sh2 sh
-> (_env_mapsto id (pshare_sh sh) v rho
<-> (_env_mapsto id (pshare_sh sh1) v * _env_mapsto id (pshare_sh sh2) v)%pred rho).