From 9d882db99633d55194e548a50689a850ce2bc166 Mon Sep 17 00:00:00 2001
From: Antoine Mathys <antoine.mathys@gmail.com>
Date: Sat, 11 Jul 2026 22:25:18 +0200
Subject: [PATCH 1/2] Add Antoine Mathys's solution to the 2025/ferguson fun
 challenge 4.

---
 2025/challenge.md | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/2025/challenge.md b/2025/challenge.md
index a28b64da65..7c38ae31f7 100644
--- a/2025/challenge.md
+++ b/2025/challenge.md
@@ -327,7 +327,7 @@ with a `-p projection` option.
 ### Fun challenge 4 for [2025/ferguson](ferguson/index.html)
 </div>
 
-This fun challenge is still **OPEN**.
+This fun challenge is **CLOSED**.
 
 Explain why `d` has to start at `-1` (bonus: experiment with different values
 and explain what happens and specifically why) and why you can't change
@@ -340,6 +340,13 @@ the `!=1` in the code:
 
 **Hint**: the above are related to each other.
 
+<div id="ferguson_4_solution">
+#### Fun challenge solution for [2025/ferguson](ferguson/index.html)
+</div>
+
+[Antoine Mathys](https://github.com/antoine-mathys) on **2026 Jul 11** presented this
+[2025/ferguson fun challenge 4 solution](https://github.com/antoine-mathys/IOCCC-2025-ferguson-fun-challenge-4).
+
 
 <div id="howe">
 ## Fun challenge for [2025/howe](howe/index.html)

From 1ab66650dcea91036fc683ed7d3804fae36bb44c Mon Sep 17 00:00:00 2001
From: Landon Curt Noll <github-mail@asthe.com>
Date: Sat, 11 Jul 2026 19:39:58 -0700
Subject: [PATCH 2/2] update 2025/challenge.html and sitemap

---
 2025/challenge.html | 7 ++++++-
 sitemap.xml         | 4 ++--
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/2025/challenge.html b/2025/challenge.html
index d9680e8211..311b8b5cc5 100644
--- a/2025/challenge.html
+++ b/2025/challenge.html
@@ -658,13 +658,18 @@ <h3 id="fun-challenge-3-for-2025ferguson">Fun challenge 3 for <a href="ferguson/
 <div id="ferguson_4">
 <h3 id="fun-challenge-4-for-2025ferguson">Fun challenge 4 for <a href="ferguson/index.html">2025/ferguson</a></h3>
 </div>
-<p>This fun challenge is still <strong>OPEN</strong>.</p>
+<p>This fun challenge is <strong>CLOSED</strong>.</p>
 <p>Explain why <code>d</code> has to start at <code>-1</code> (bonus: experiment with different values
 and explain what happens and specifically why) and why you can’t change
 the <code>!=1</code> in the code:</p>
 <pre><code>    if  (d=(c!=e==!d!=d!=d==1&amp;&amp;e!=c)!=1||/* NOW YOU KNOW d IS 1! */fread(c, -*(S[F])-d*3 ,
         b*j,q)^j *j *2)X;</code></pre>
 <p><strong>Hint</strong>: the above are related to each other.</p>
+<div id="ferguson_4_solution">
+<h4 id="fun-challenge-solution-for-2025ferguson">Fun challenge solution for <a href="ferguson/index.html">2025/ferguson</a></h4>
+</div>
+<p><a href="https://github.com/antoine-mathys">Antoine Mathys</a> on <strong>2026 Jul 11</strong> presented this
+<a href="https://github.com/antoine-mathys/IOCCC-2025-ferguson-fun-challenge-4">2025/ferguson fun challenge 4 solution</a>.</p>
 <div id="howe">
 <h2 id="fun-challenge-for-2025howe">Fun challenge for <a href="howe/index.html">2025/howe</a></h2>
 </div>
diff --git a/sitemap.xml b/sitemap.xml
index e986d7b7db..9ccad3593b 100644
--- a/sitemap.xml
+++ b/sitemap.xml
@@ -15994,11 +15994,11 @@
 </url>
 <url>
     <loc>https://www.ioccc.org/2025/challenge.html</loc>
-    <lastmod>2026-07-10T16:42:52+00:00</lastmod>
+    <lastmod>2026-07-12T02:38:02+00:00</lastmod>
 </url>
 <url>
     <loc>https://www.ioccc.org/2025/challenge.md</loc>
-    <lastmod>2026-07-10T16:35:52+00:00</lastmod>
+    <lastmod>2026-07-12T02:37:04+00:00</lastmod>
 </url>
 <url>
     <loc>https://www.ioccc.org/2025/diels-grabsch/2025_diels-grabsch.tar.bz2</loc>