diff --git a/theories/properties.v b/theories/properties.v
index c277856..6523707 100644
--- a/theories/properties.v
+++ b/theories/properties.v
@@ -1,5 +1,5 @@
 Require Import Autosubst2.syntax
-               Autosubst2.core Autosubst2.unscoped typing ssreflect List.
+               Autosubst2.core Autosubst2.unscoped typing ssreflect List ssrbool.
 
 From Hammer Require Import Tactics.
 
@@ -39,6 +39,18 @@ End ren.
 
 Arguments ren_ok {T}.
 
+Definition bool_leb a b :=
+  match a,b with
+  | true, false => false
+  | _,_ => true
+  end.
+
+Lemma bool_leb_refl a : bool_leb a a.
+Proof. case : a => //=. Qed.
+
+Lemma bool_le_spec a b : Bool.reflect (Bool.le a b) (bool_leb a b).
+Proof. hauto l:on inv:bool ctrs:Bool.reflect. Qed.
+
 Module Liftable.
   Lemma lookup_fixed i Γ ℓ A :
     lookup i Γ (ℓ, A) ->
@@ -74,11 +86,92 @@ Module Liftable.
   Proof.
     elim : a ξ Φ Ψ => //=; hauto l:on use:ren_up unfold:ren_ok.
   Qed.
+
+  Fixpoint ctx_leq Φ Ψ :=
+    match Φ, Ψ with
+    | nil, nil => true
+    | ℓ::Φ, ℓ'::Ψ => bool_leb ℓ ℓ' && ctx_leq Φ Ψ
+    | _, _ => false
+    end.
+
+  Lemma ctx_leq_lookup Φ Ψ i ℓ1 :
+    ctx_leq Φ Ψ ->
+    lookup i Ψ ℓ1 ->
+    exists ℓ0, lookup i Φ ℓ0 /\
+    Bool.le ℓ0 ℓ1.
+  Proof.
+    move => + h. move : Φ.
+    elim : i Ψ ℓ1 / h.
+    - move => A Γ Ψ h.
+      case : Ψ h => //=.
+      move => B Ψ.
+      case : bool_le_spec => //=.
+      sfirstorder ctrs:lookup.
+    - move => i Γ A B hi ihi Ψ.
+      case : Ψ => //=.
+      move => C Ψ.
+      case : bool_le_spec => //=.
+      hauto lq:on ctrs:lookup.
+  Qed.
+
+  Lemma narrowing Φ Ψ a :
+    ctx_leq Φ Ψ ->
+    liftable Ψ a ->
+    liftable Φ a.
+  Proof.
+    elim : a Φ Ψ => //=.
+    - move => n Φ Ψ.
+      move : ctx_leq_lookup; repeat move/[apply].
+      move => [ℓ1 [h0 h1]].
+      suff : ℓ1 = false by congruence.
+      hauto q:on inv:bool.
+    - sfirstorder.
+    - sfirstorder.
+    - sfirstorder.
+  Qed.
+
 End Liftable.
 
 
+Definition lvl_leb a b :=
+  match a, b with
+  | Fixed ℓ0, Fixed ℓ1 => Bool.eqb ℓ0 ℓ1
+  | Floating ℓ0, Floating ℓ1 => bool_leb ℓ0 ℓ1
+  | _,_ => false
+  end.
+
+Lemma lvl_leb_refl a : lvl_leb a a.
+Proof. destruct a,b; sfirstorder use:Bool.eqb_reflx, bool_leb_refl. Qed.
+
 Module Typing.
 
+  Inductive ctx_fleq : list bool -> ctx -> ctx -> Prop :=
+  | FL_Nil : ctx_fleq nil nil nil
+  | FL_ConsFixed Φ Γ Δ A :
+    ctx_fleq Φ Γ Δ ->
+    ctx_fleq (false :: Φ) (A :: Γ) (A :: Δ)
+  | FL_ConsFloat Φ Γ Δ ℓ0 ℓ1 A :
+    ctx_fleq Φ Γ Δ ->
+    lvl_leb ℓ0 ℓ1 ->
+    ctx_fleq (true :: Φ) ((ℓ0, A) :: Γ) ((ℓ1, A) :: Δ).
+
+  Lemma ctx_fleq_fixed Φ Γ Δ :
+    ctx_fleq Φ Γ Δ ->
+    ctx_fleq (fixed_ctx Γ) Γ Δ.
+  Proof.
+    move => h. elim : Φ Γ Δ/ h => //=.
+    - constructor.
+    - move => Φ Γ Δ [ℓ B].
+      move => h0 h1.
+      destruct ℓ => //=; constructor; eauto using lvl_leb_refl.
+    - move => Φ Γ Δ ℓ0 ℓ1 A hctx ihctx h0.
+      destruct ℓ0, ℓ1 => //=.
+      simpl in h0.
+      move : h0. case : Bool.eqb_spec => //= ? _. subst.
+      by constructor.
+      by constructor.
+  Qed.
+
   Lemma renaming ξ Γ Δ ℓ a A  :
     Δ ⊢ a ;; ℓ  ∈ A  ->
     ren_ok ξ Γ Δ ->
@@ -96,11 +189,51 @@ Module Typing.
     - hauto lq:on ctrs:Wt use:ren_up.
   Qed.
 
-  (* Liftable: stable *)
-(* If a well-typed term is liftable, then it should remain well-typed at the same level
-if the floating variables are lifted  *)
+  Lemma ctx_fleq_lookup i Φ (Γ Δ  : ctx) A  :
+    ctx_fleq Φ Γ Δ ->
+    lookup i Φ false ->
+    lookup i Γ A ->
+    lookup i Δ A.
+  Proof.
+    move => h. move : A i.
+    elim : Φ Γ Δ / h => //=; sauto.
+  Qed.
 
-  (* Upgrade *)
-  (* If Γ ⊢ a ;; ℓ ∈ A, we want to lift up the levels in Γ  *)
+  Lemma ctx_fleq_fixed_eq Φ Γ Δ :
+    ctx_fleq Φ Γ Δ ->
+    fixed_ctx Γ = fixed_ctx Δ.
+  Proof.
+    move => h. elim : Φ Γ Δ / h => //=.
+    - hauto lq:on.
+    - move => Φ Γ Δ ℓ0 ℓ1 h ih h0 h1.
+      f_equal => //.
+      move {h0 ih h}.
+      hauto lq:on inv:Level.
+  Qed.
+
+  Lemma upgrading Φ Γ Δ a ℓ A :
+    Γ ⊢ a ;; ℓ ∈ A ->
+    liftable Φ a ->
+    ctx_fleq Φ Γ Δ ->
+    Δ ⊢ a ;; ℓ ∈ A.
+  Proof.
+    move => h. move : Φ Δ.
+    elim : Γ a ℓ A /h.
+    - move => Γ ℓ i ℓ0 A hℓ hi Φ Δ /= h0 h1.
+      econstructor; eauto.
+      eauto using ctx_fleq_lookup.
+    - hauto lq:on ctrs:Wt.
+    - move => Γ ℓ a A B ha iha Φ Δ hla hleq /=.
+      constructor. apply : iha => /=; cycle 1; eauto.
+      by constructor.
+    - move => Γ ℓ ℓ0 a b A B hb ihb ha iha hla Φ Δ /= hlb hctx.
+      apply : T_App; eauto.
+      apply : iha; eauto.
+      sfirstorder use:ctx_fleq_fixed.
+      erewrite <- ctx_fleq_fixed_eq; eauto.
+    - move => Γ ℓ ℓ0 b A B hb ihb Δ /=.
+      move => h0 h1. constructor. apply : ihb; eauto.
+      simpl. by constructor.
+  Qed.
 
 End Typing.