diff --git a/CLAUDE.md b/CLAUDE.md
index e1a079729..843464021 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -6,6 +6,10 @@ Project guidance for Claude Code (CLI, IDE, and the GitHub Action). The same con
 
 `mds` holds the mathematics that the Morrison-Lab data science courses assume: notation, algebra, calculus, linear algebra and vector calculus, as [Quarto](https://quarto.org/) fragments. It renders on its own as a website, and course sites such as `mlds` link to its pages by URL, so a page's path and its `#id` anchors are an interface: renaming either breaks those links. The scaffolding came from the UCD-SERG `qwt` template.
 
+The shared math basics (logic and proof writing, sets, functions, number systems, relations, induction, growth rates, expressions and algorithms, notation) moved to [`Morrison-Lab/mcs`](https://github.com/Morrison-Lab/mcs), the first site in the course sequence (Morrison-Lab/mcs#60).
+The matching `mds` pages are redirect stubs.
+Link to the `mcs` page, and add new content on those topics to `mcs`, not here.
+
 Authoritative style guide: [UCD-SERG Lab Manual](https://ucd-serg.github.io/lab-manual/) (source: <https://github.com/UCD-SERG/lab-manual>).
 
 ## Repository layout