∀ {L : FirstOrder.Language} {M : Type w} [inst : L.Structure M] {α : Type u'} {β : Type v'}
  [inst_1 : (L.withConstants α).Structure M] [(L.lhomWithConstants α).IsExpansionOn M] {n : ℕ}
  {t : (L.withConstants α).Term (β ⊕ Fin n)} {v : β → M} {xs : Fin n → M},
  FirstOrder.Language.Term.realize (Sum.elim (Sum.elim (fun a => ↑(L.con a)) v) xs)
      (FirstOrder.Language.Term.constantsVarsEquivLeft t) =
    FirstOrder.Language.Term.realize (Sum.elim v xs) t