diff --git a/articles/links-of-the-open-world-programmer/page.mmd b/articles/links-of-the-open-world-programmer/page.mmd
index 37c3d98..36daf7c 100644
--- a/articles/links-of-the-open-world-programmer/page.mmd
+++ b/articles/links-of-the-open-world-programmer/page.mmd
@@ -59,7 +59,6 @@ CSS:    /style.css
 - [Line and circle rasterization](http://www.sunshine2k.de/coding/java/Bresenham/RasterisingLinesCircles.pdf)
 - [Occlusion culling of Vintage Story](https://github.com/tyronx/occlusionculling)
 - [Minecraft work on cave occlusion, in 2 parts](https://tomcc.github.io/2014/08/31/visibility-1.html)
-- [Awesome article on hashtables](https://thenumb.at/Hashtables/)
 - [Order independent blending technique](https://jcgt.org/published/0002/02/09/)
 - [High performance voxel engine](https://nickmcd.me/2021/04/04/high-performance-voxel-engine/)
 - [Monotone meshing](https://blackflux.wordpress.com/tag/monotone-meshing/)
@@ -98,3 +97,9 @@ CSS:    /style.css
 - [Granular buffer memory control](https://registry.khronos.org/OpenGL/extensions/ARB/ARB_sparse_buffer.txt)
 - [Window pos](https://people.freedesktop.org/~marcheu/extensions/ARB/window_pos.html)
 - [Optimized fixed function fog](https://people.freedesktop.org/~marcheu/extensions/doc/fog_coord.html)
+
+## data representations
+- [Efficient varying-length integers](https://john-millikin.com/vu128-efficient-variable-length-integers)
+- [Awesome article on hashtables](https://thenumb.at/Hashtables/)
+- [Crit-bit trees](https://cr.yp.to/critbit.html)
+- [QP tries](https://dotat.at/prog/qp/README.html)