diff --git a/cosn.v b/cosn.v
index 4b75918..e2506a2 100644
--- a/cosn.v
+++ b/cosn.v
@@ -9,6 +9,7 @@ Require Import Psatz.
 From stdpp Require Import relations (rtc (..), rtc_once, rtc_r, sn).
 From Hammer Require Import Tactics.
 Require Import Autosubst2.core Autosubst2.unscoped Autosubst2.syntax common fp_red.
+Require Import Btauto.
 
 Fixpoint nostuck (a : PTm) :=
   match a with
@@ -20,18 +21,19 @@ Fixpoint nostuck (a : PTm) :=
   | PProj _ a => (ishf a ==> ispair a) && nostuck a
   | PZero => true
   | PSuc a => nostuck a
-  | PInd P a b c => (ishf a ==> iszero a || issuc a) && nostuck b && nostuck c
+  | PInd P a b c => nostuck P && (ishf a ==> iszero a || issuc a) && nostuck b && nostuck c
   | PNat => true
   | PUniv _ => true
   end.
 
 
 CoInductive safe a : Prop :=
-  safe_intro {safe_ok : nostuck a; safe_red : forall b,RRed.R a b -> safe b}.
+  safe_intro :
+    nostuck a ->
+    (forall b,RRed.R a b -> safe b) ->
+    safe a.
 
 Arguments safe_intro {a}.
-Arguments safe_ok {a}.
-Arguments safe_red {a}.
 
 Lemma safe_coind P : (forall a, P a -> nostuck a /\  (forall b, RRed.R a b -> P b)) ->  forall a, P a -> safe a.
   move => h.
@@ -42,3 +44,64 @@ Lemma safe_coind P : (forall a, P a -> nostuck a /\  (forall b, RRed.R a b -> P
   apply ha0.
   move => b hb. apply ha1 in hb. apply ih. apply hb.
 Qed.
+
+Lemma safe_app_inv0  : forall a b, safe (PApp a b) -> safe a.
+Proof.
+  suff : forall a, (exists b, safe (PApp a b)) -> safe a by firstorder.
+  apply safe_coind.
+  sauto lqb:on.
+Qed.
+
+Lemma safe_app_inv1  : forall a b, safe (PApp a b) -> safe b.
+Proof.
+  suff : forall b, (exists a, safe (PApp a b)) -> safe b by firstorder.
+  apply safe_coind.
+  sauto lqb:on.
+Qed.
+
+Lemma safe_abs_inv : forall a, safe (PAbs a) -> safe a.
+Proof.
+  apply safe_coind.
+  sauto lqb:on.
+Qed.
+
+Lemma nostuck_antisubstitution : forall ρ a, nostuck (subst_PTm ρ a) -> nostuck a.
+Proof.
+  suff : forall (ρ : nat -> PTm) (a : PTm), nostuck (subst_PTm ρ a) ==> nostuck a by sauto lqb:on.
+  move => /[swap]. elim => //=.
+  - move => *. rewrite !Bool.implb_orb /is_true. btauto.
+  - move => b ihb a iha ρ.
+    move /(_ ρ) : ihb. apply /implyP.
+    move /(_ ρ) : iha. apply /implyP.
+    case : b => //= *; rewrite /is_true !Bool.implb_orb; btauto.
+  - move => a iha b ihb ρ.
+    move /(_ ρ) : ihb. apply /implyP.
+    move /(_ ρ) : iha. apply /implyP.
+    rewrite /is_true !Bool.implb_orb; btauto.
+  - move => p u hu ρ.
+    move /(_ ρ) : hu. apply /implyP.
+    case : u => //= *; rewrite /is_true !Bool.implb_orb; btauto.
+  - move => _ a iha b ihb ρ.
+    move /(_ (up_PTm_PTm ρ)) : ihb. apply /implyP.
+    move /(_ ρ) : iha. apply /implyP.
+    rewrite /is_true !Bool.implb_orb; btauto.
+  - move => P ihP a iha b ihb c ihc ρ.
+    move /(_ (up_PTm_PTm ρ)) : ihP. apply /implyP.
+    move /(_ ρ) : iha. apply /implyP.
+    move /(_ ρ) : ihb. apply /implyP.
+    move /(_ (up_PTm_PTm (up_PTm_PTm ρ))) : ihc. apply /implyP.
+    case : a => //= *; rewrite /is_true !Bool.implb_orb; btauto.
+Qed.
+
+Lemma safe_antisubstitution : forall ρ a, safe (subst_PTm ρ a) -> safe a.
+Proof.
+  suff : forall a, (exists ρ, safe (subst_PTm ρ a)) -> safe a by firstorder.
+  apply safe_coind.
+  move => a [ρ ha].
+  split.
+  have {}ha : nostuck (subst_PTm ρ a) by hauto lq:on inv:safe lq:on.
+  by eauto using nostuck_antisubstitution.
+  move => b hr. exists ρ.
+  inversion ha as [ha0 ha1].
+  hauto lq:on use:RRed.substing.
+Qed.
diff --git a/theories/fp_red.v b/theories/fp_red.v
index 507eb5a..a3fb270 100644
--- a/theories/fp_red.v
+++ b/theories/fp_red.v
@@ -1270,7 +1270,7 @@ Module Type NoForbid.
 
   Axiom P_PairInv : forall (a b : PTm), P (PPair a b) -> P a /\ P b.
   Axiom P_ProjInv : forall p (a : PTm), P (PProj p a) -> P a.
-  Axiom P_renaming : forall (ξ : nat -> nat) a , P (ren_PTm ξ a) <-> P a.
+  Axiom P_renaming : forall (ξ : nat -> nat) a , P (ren_PTm ξ a) -> P a.
 End NoForbid.
 
 Module Type NoForbid_FactSig (M : NoForbid).
@@ -1342,7 +1342,7 @@ Module SN_NoForbid <: NoForbid.
     induction h; sauto lq:on rew:off.
   Qed.
 
-  Lemma P_renaming : forall (ξ : nat -> nat) a , P (ren_PTm ξ a) <-> P  a.
+  Lemma P_renaming : forall (ξ : nat -> nat) a , P (ren_PTm ξ a) -> P  a.
   Proof. hauto lq:on use:sn_antirenaming, sn_renaming. Qed.
 
   Lemma P_ProjBind : forall p p' (A : PTm) B, ~ P (PProj p (PBind p' A B)).