From 6d10b7594f487bdfbef99d05bda34405dd85c8b8 Mon Sep 17 00:00:00 2001
From: Andreas Grois <andi@grois.info>
Date: Sun, 16 Nov 2025 14:24:46 +0100
Subject: Lean 4.23

---
 Day9.lean | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

(limited to 'Day9.lean')

diff --git a/Day9.lean b/Day9.lean
index 8fc449c..ac8edd8 100644
--- a/Day9.lean
+++ b/Day9.lean
@@ -31,7 +31,7 @@ private def extrapolate : List Int → Int
     0
   else
     have : (differences (a :: as)).length < as.length + 1 := by
-      simp +arith[differences]
+      simp +arith
       induction (as) <;> simp +arith[differences]
       case cons b bs hb => rw[←differences_length_independent_arg]
                            assumption
-- 
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