diff --git a/_quarto-website.yml b/_quarto-website.yml
index 914447684..407c01bd2 100644
--- a/_quarto-website.yml
+++ b/_quarto-website.yml
@@ -70,6 +70,10 @@ website:
           - algebra-exponentials.qmd
           - algebra-trigonometry.qmd
           - algebra-complex.qmd
+      - text: "Proof Writing"
+        href: proof-writing.qmd
+      - text: "Induction and Recursion"
+        href: induction.qmd
       - text: "Measures"
         menu:
           - text: "Overview"
@@ -113,10 +117,6 @@ website:
           - optimization-newton.qmd
           - optimization-gradient-descent.qmd
           - optimization-quasi-newton.qmd
-      - text: "Proof Writing"
-        href: proof-writing.qmd
-      - text: "Induction and Recursion"
-        href: induction.qmd
     right:
       - icon: github
         href: https://github.com/Morrison-Lab/mds
@@ -155,6 +155,8 @@ website:
           - algebra-exponentials.qmd
           - algebra-trigonometry.qmd
           - algebra-complex.qmd
+      - proof-writing.qmd
+      - induction.qmd
       - section: "Measures"
         href: measures.qmd
         contents:
@@ -193,8 +195,6 @@ website:
           - optimization-newton.qmd
           - optimization-gradient-descent.qmd
           - optimization-quasi-newton.qmd
-      - proof-writing.qmd
-      - induction.qmd
 
 # Each type below gets a title bar (type, number, name) apart from the body,
 # and folds, open by default: the callouty-theorem defaults since 1.4.0.
diff --git a/index.qmd b/index.qmd
index 1b2b84c71..15a92d608 100644
--- a/index.qmd
+++ b/index.qmd
@@ -24,7 +24,14 @@ mathematical notation, algebra
 (including exponentials and logarithms),
 univariate calculus, linear algebra, vector calculus, optimization, and proof writing.
 Some key results are listed here,
-organized by topic:
+organized by topic.
+
+The first six topics are the foundations.
+Apart from a few remarks in Algebra that touch on calculus,
+they assume no calculus,
+so a course on discrete math,
+such as [Math for Computer Science](https://morrison-lab.github.io/mcs/),
+can build on them directly:
 
 - [Notation](notation.qmd):
   common symbols
@@ -46,6 +53,13 @@ organized by topic:
 - [Algebra](algebra.qmd):
   equalities and [inequalities](proof-writing.qmd#def-inequality), infimum and supremum,
   percent, sums, products, quotients, limits of sums, notational shorthands, exponentials and logarithms
+- [Proof Writing](proof-writing.qmd):
+  propositions, quantifiers, proofs and derivations, and showing and annotating every step of a [derivation](proof-writing.qmd#def-derivation)
+- [Induction and Recursion](induction.qmd):
+  [recursively defined sequences](induction.qmd#def-recursive-sequence) and [strong induction](induction.qmd#def-strong-induction)
+
+The remaining topics build on the foundations and on each other:
+
 - [Measures](measures.qmd):
   $\sigma$-algebras, [finite](functions.qmd#def-finite-set) and [countable additivity](measures.qmd#def-countable-additivity),
   measures, and the counting measure
@@ -65,8 +79,6 @@ organized by topic:
 - [Optimization](optimization.qmd):
   optimality conditions, Taylor approximations, convexity in several variables,
   Lagrange multipliers, Newton's method, and gradient descent
-- [Proof Writing](proof-writing.qmd):
-  propositions, quantifiers, proofs and derivations, and showing and annotating every step of a [derivation](proof-writing.qmd#def-derivation)
 
 # Further reading {.unnumbered}