From e60ece956a560f51b169689aa8ba263cfa096445 Mon Sep 17 00:00:00 2001
From: Vectornaut <vectornaut@nobody@nowhere.net>
Date: Sat, 23 Aug 2025 16:26:17 +0000
Subject: [PATCH] Add crystal structures

---
 Test-problems.md | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/Test-problems.md b/Test-problems.md
index 16cf674..dd1a5f9 100644
--- a/Test-problems.md
+++ b/Test-problems.md
@@ -381,4 +381,16 @@ $$s + t = 1 + \tfrac{1}{2} st$$
 
 #### Note
 
-[Geometry Expressions](https://geometryexpressions.com) can solve this problem handily!
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+[Geometry Expressions](https://geometryexpressions.com) can solve this problem handily!
+
+## Other ambient geometries
+
+### Crystal structures
+
+#### Source
+
+Peter Fenyes
+
+#### Statement
+
+Assemble triply periodic sphere packings like the ones sometimes used to illustrate [crystal structures](https://chem.libretexts.org/Courses/East_Tennessee_State_University/CHEM_3110%3A_Descriptive_Inorganic_Chemistry/05%3A_Structure_and_Energetics_of_Solids/5.01%3A_Crystal_Structures_and_Unit_Cells).
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