diff --git a/plans/datalog-on-sx.md b/plans/datalog-on-sx.md
index 65bd65ac..f0233eec 100644
--- a/plans/datalog-on-sx.md
+++ b/plans/datalog-on-sx.md
@@ -277,6 +277,11 @@ large graphs.
 
 _Newest first._
 
+- 2026-05-08 — Demo: tag co-occurrence. `(cotagged P T1 T2)` — post
+  has both T1 and T2 with T1 != T2 — and `(tag-pair-count T1 T2 N)`
+  counting posts per distinct tag pair. Demonstrates count
+  aggregation grouped by outer-context vars. 2 new demo tests.
+
 - 2026-05-08 — `dl-query` accepts a list of body literals for
   conjunctive queries, in addition to a single positive literal.
   `dl-query-coerce` dispatches based on the first element's shape: