Expr Γ Δ ξ (tbranches @@ l)
| ELetRec : ∀ Γ Δ ξ l τ vars, let ξ' := update_ξ ξ (map (fun x => ((fst x),(snd x @@ l))) (leaves vars)) in
Expr Γ Δ ξ (tbranches @@ l)
| ELetRec : ∀ Γ Δ ξ l τ vars, let ξ' := update_ξ ξ (map (fun x => ((fst x),(snd x @@ l))) (leaves vars)) in