From 7f31a2c0353d31f05e7a9f00421a35141e127f5b Mon Sep 17 00:00:00 2001
From: bt3gl <1130416+bt3gl@users.noreply.github.com>
Date: Thu, 29 Sep 2022 04:40:22 -0700
Subject: [PATCH] =?UTF-8?q?=F0=9F=8D=9F?=
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---
 solidity/saving_gas.md | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/solidity/saving_gas.md b/solidity/saving_gas.md
index 8c682d9..12db511 100644
--- a/solidity/saving_gas.md
+++ b/solidity/saving_gas.md
@@ -115,6 +115,18 @@ uint256 world; //good, cheap
 
 <br>
 
+---
+
+<br>
+
+## negative gas costs
+
+- Deleting a contract (SELFDESTRUCT) is worth a refund of 24,000 gas.
+- Changing a storage address from a nonzero value to zero (SSTORE[x] = 0) is worth a refund of 15,000 gas.
+
+<br>
+
+
 ---
 
 ## resources and tools