diff --git a/src/teaching/cse-562/2019sp/index.erb b/src/teaching/cse-562/2019sp/index.erb
index c4946820..c813b18f 100644
--- a/src/teaching/cse-562/2019sp/index.erb
+++ b/src/teaching/cse-562/2019sp/index.erb
@@ -186,7 +186,8 @@ schedule:
       slides: "slide/2019-04-24-Provenance.html"
   - date: "Apr 26"
     topic: "Provenance Semirings"
-    textbook: "Ch. 23.4"
+    materials:
+      slides: "slide/2019-04-26-ProvenanceSemirings.html"
   - date: "Apr 29"
     topic: "Implementing Provenance Queries"
     textbook: "Ch. 23.5"