Class Ghost := { G : Type; valid : G -> Prop;
  Join_G :> Join G; Sep_G :> Sep_alg G; Perm_G :> Perm_alg G;
  join_valid : forall a b c, join a b c -> valid c -> valid a }.Class Ghost := { G : Type; valid : G -> Prop;
  Join_G :> Join G; Sep_G :> Sep_alg G; Perm_G :> Perm_alg G;
  join_valid : forall a b c, join a b c -> valid c -> valid a }.Class Ghost := { G : Type; valid : G -> Prop;
  Join_G :> Join G; Sep_G :> Sep_alg G; Perm_G :> Perm_alg G;
  join_valid : forall a b c, join a b c -> valid c -> valid a }.Class Ghost := { G : Type; valid : G -> Prop;
  Join_G :> Join G; Sep_G :> Sep_alg G; Perm_G :> Perm_alg G;
  join_valid : forall a b c, join a b c -> valid c -> valid a }.Class Ghost := { G : Type; valid : G -> Prop;
  Join_G :> Join G; Sep_G :> Sep_alg G; Perm_G :> Perm_alg G;
  join_valid : forall a b c, join a b c -> valid c -> valid a }.Class Ghost := { G : Type; valid : G -> Prop;
  Join_G :> Join G; Sep_G :> Sep_alg G; Perm_G :> Perm_alg G;
  join_valid : forall a b c, join a b c -> valid c -> valid a }.Class Ghost := { G : Type; valid : G -> Prop;
  Join_G :> Join G; Sep_G :> Sep_alg G; Perm_G :> Perm_alg G;
  join_valid : forall a b c, join a b c -> valid c -> valid a }.

(* Specifications: *)
Lemma core_valid: forall a, valid a -> valid (core a).