diff --git a/IV/bib.bib b/IV/bib.bib
index 155ba13..3647a8d 100644
--- a/IV/bib.bib
+++ b/IV/bib.bib
@@ -221,3 +221,10 @@
   url={https://postgis.net/docs/reference.html},
   urldate={2021-05-12},
 }
+
+@online{wmsql,
+  author={Motiejus Jakštys},
+  title={Wang--M{\"u}ller implementation in PostGIS},
+  url={https://github.com/motiejus/wm},
+  urldate={2021-05-19},
+}