(* ---------------------------------------------- *)

Lemma An_IsoRefl2_derivable  : ∀ (G : context) (D : available_props) (phi1 phi2 : constraint),
AnnPropWff G phi1
→ AnnPropWff G phi2
→ erase_constraint phi1 = erase_constraint phi2 →
exists g,
AnnIso G D g phi1 phi2.