diff --git a/2021-06-15.md b/2021-06-15.md
index 043c38278..ccc51e305 100644
--- a/2021-06-15.md
+++ b/2021-06-15.md
@@ -9,6 +9,8 @@
 - [[functions]]
 	- [[interesting functions]]
 		- [[dirichlet function]]
+			- 
 		- [[thomae's function]]
 		- [[cantor function]]
-		- [[]]
\ No newline at end of file
+		- [[weierstrass function]]
+			- one of the first [[fractal]] curve studied
\ No newline at end of file