Axiom set_reif_eq2 :
forall i tus tvs typ vr tr val,
exprD' tus tvs (typtree typ) tr = Some val ->
exprD' tus tvs (typtree typ) (App (App (Inj (inr (Data (fset typ i)))) vr) tr)  =
exprD' tus tvs (typtree typ) (get_set_reif.set_reif i vr tr typ).

Lemma replace_set_sound : forall tus tvs e, exprD' tus tvs typrop e = exprD' tus tvs typrop (replace_set e).