(* Instance Iso_atoms_sub_mor : Morphisms.Proper (eq ==> AtomSetImpl.Subset ==> eq ==> eq ==> impl) Iso.  Instance DefEq_atoms_sub_mor : Morphisms.Proper (eq ==> AtomSetImpl.Subset ==> eq ==> eq ==> eq ==> impl) DefEq. *)

Lemma DefEq_weaken_available :
forall G D A B T, DefEq G D A B T -> DefEq G (dom G) A B T.