From 2a9261d1ba962deff9fcc1784be44563af513af5 Mon Sep 17 00:00:00 2001
From: Andreas Grois <andi@grois.info>
Date: Fri, 10 Oct 2025 00:30:19 +0200
Subject: Lean 4.18

---
 Day9.lean | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

(limited to 'Day9.lean')

diff --git a/Day9.lean b/Day9.lean
index d024823..8fc449c 100644
--- a/Day9.lean
+++ b/Day9.lean
@@ -31,8 +31,8 @@ private def extrapolate : List Int → Int
     0
   else
     have : (differences (a :: as)).length < as.length + 1 := by
-      simp_arith[differences]
-      induction (as) <;> simp_arith[differences]
+      simp +arith[differences]
+      induction (as) <;> simp +arith[differences]
       case cons b bs hb => rw[←differences_length_independent_arg]
                            assumption
     a + extrapolate (differences (a :: as))
-- 
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