1 files changed, 1 insertions, 1 deletions
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