Update index.md

Author: tobideusser

teaching/ilsds25/index.md

@@ -57,6 +57,7 @@ Practical Examples will serve as a capstone to the course, where students will e
 ### Lecture Slides
 
 - [Lecture 1](https://github.com/AppliedMachineLearning-Lab/ilsds/raw/refs/heads/main/ILSDS_WS25_Part_1_Intro.pdf.zip)
+- [Lecture 2 - 4](https://github.com/AppliedMachineLearning-Lab/ilsds/raw/refs/heads/main/ILSDS_WS25_Part_2_MathCores.pdf.zip)
 
 ### Assignments