diff --git a/theories/list_numbers.v b/theories/list_numbers.v
index 11c1bb1718860a0e0fdf3275dabbcffe1282bab2..d41a94f81011864bfa2bb4fb12a0d59f075b990f 100644
--- a/theories/list_numbers.v
+++ b/theories/list_numbers.v
@@ -201,10 +201,7 @@ Section sum_list.
     induction l; simpl; rewrite ?reverse_cons, ?sum_list_with_app; simpl; lia.
   Qed.
   Lemma sum_list_with_in x (f : A → nat) l : x ∈ l → f x ≤ sum_list_with f l.
-  Proof.
-    intros H. induction H.
-    all: simpl; lia.
-  Qed.
+  Proof. induction 1; simpl; lia. Qed.
   Lemma join_reshape szs l :
     sum_list szs = length l → mjoin (reshape szs l) = l.
   Proof.