From 17fcce7944a4587bc1c801bbd2ea16db64fdd979 Mon Sep 17 00:00:00 2001
From: "aleph-prover-test[bot]"
 <247855025+aleph-prover-test[bot]@users.noreply.github.com>
Date: Tue, 18 Aug 2026 18:27:35 +0000
Subject: [PATCH] Proof for eq_four

Automated commit at 20260818_182733
---
 EasyLean/Basic.lean | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/EasyLean/Basic.lean b/EasyLean/Basic.lean
index 305e1ca..81c716d 100644
--- a/EasyLean/Basic.lean
+++ b/EasyLean/Basic.lean
@@ -9,4 +9,5 @@ theorem mathd_algebra_513
   sorry
 
 theorem eq_four : ∀ a b c d : Nat, a = b → a = d → a = c → c = b := by
-  sorry
+  intro a b c d hab had hac
+  exact hac.symm.trans hab