diff --git a/slides/pages/qa.md b/slides/pages/qa.md
index 446e96d236dcca35ab752ed916c07363dac60e89..9ac2a45983e9f0ba3201b16b1d38add6d6499a99 100644
--- a/slides/pages/qa.md
+++ b/slides/pages/qa.md
@@ -11,4 +11,7 @@ Any questions about:
 - Topics from the lectures
 - Organisation
 
-<br/>
+### References
+
+- [Petri Nets in Snoopy](https://link.springer.com/protocol/10.1007/978-1-61779-361-5_21)
+- [Modeling Business Processes: A Petri Net-Oriented Approach](https://direct.mit.edu/books/book/2268/Modeling-Business-ProcessesA-Petri-Net-Oriented)