Remove the repeated title heading from five split-out pages

_functions.qmd

@@ -9,7 +9,7 @@ The functions here go between the sets defined on the [Sets](sets.qmd) page.
 
 :::
 
-## Functions
+[]{#functions}
 
 {{< include mds/_subfiles/functions/_def-function.qmd >}}
 

_sets-functions.qmd

@@ -3,10 +3,17 @@ include mds/_sets-functions.qmd keep rendering. It includes the three fragments
 replaced it, one after another. Each fragment includes the macros and opens with its own
 introduction, so in a host page each introduction follows the previous fragment's last
 section and links to pages (sets.qmd and the others) that the host may not have. No host
-site includes this shim today; new host pages should include the three fragments directly. -->
+site includes this shim today; new host pages should include the three fragments directly.
+The sets and functions fragments no longer open with a section heading,
+so a host page that includes them writes its own Sets and Functions headings;
+the shim writes them here, with ids that differ from the fragments' own anchors. -->
+
+## Sets {#sec-shim-sets}
 
 {{< include mds/_sets.qmd >}}
 
+## Functions {#sec-shim-functions}
+
 {{< include mds/_functions.qmd >}}
 
 {{< include mds/_expressions-algorithms.qmd >}}

_sets.qmd

@@ -11,7 +11,7 @@ the expressions that write functions down and the algorithms that compute them.
 
 :::
 
-## Sets
+[]{#sets}
 
 {{< include mds/_subfiles/sets/_def-set.qmd >}}
 

indicator-functions.qmd

@@ -8,6 +8,8 @@ format:
     output-file: indicator-functions-handout.pdf
   docx:
     output-file: indicator-functions.docx
+filters:
+  - split-page-headings.lua
 ---
 
 {{< include mds/_indicator-functions.qmd >}}

linear-algebra-matrices.qmd

@@ -8,6 +8,8 @@ format:
     output-file: linear-algebra-matrices-handout.pdf
   docx:
     output-file: linear-algebra-matrices.docx
+filters:
+  - split-page-headings.lua
 ---
 
 {{< include latex-macros/macros.qmd >}}

linear-algebra-vectors.qmd

@@ -8,6 +8,8 @@ format:
     output-file: linear-algebra-vectors-handout.pdf
   docx:
     output-file: linear-algebra-vectors.docx
+filters:
+  - split-page-headings.lua
 ---
 
 {{< include latex-macros/macros.qmd >}}

split-page-headings.lua

@@ -0,0 +1,35 @@
+-- For a page that renders one section fragment on its own.
+-- The fragment opens with a level 2 heading that repeats the page title,
+-- because the combined Linear Algebra page includes the same fragment as a section.
+-- Drop that heading and move every later heading deeper than level 2 up one level,
+-- so the page body starts at level 2 under the title.
+-- The fragments that use this filter have no other level 2 heading.
+function Pandoc(doc)
+  local title = pandoc.utils.stringify(doc.meta.title or "")
+  local dropped = false
+  local blocks = pandoc.List()
+  for _, block in ipairs(doc.blocks) do
+    if block.t == "Header" then
+      if not dropped and block.level == 2
+        and pandoc.utils.stringify(block.content):lower() == title:lower() then
+        dropped = true
+        -- Keep the heading's id as an empty anchor so links to it still work.
+        if block.identifier ~= "" then
+          blocks:insert(pandoc.Para({pandoc.Span({}, pandoc.Attr(block.identifier))}))
+        end
+      else
+        if dropped and block.level > 2 then
+          block.level = block.level - 1
+        end
+        blocks:insert(block)
+      end
+    else
+      blocks:insert(block)
+    end
+  end
+  if not dropped then
+    io.stderr:write("split-page-headings.lua: no level 2 heading matches the title '" .. title .. "'\n")
+  end
+  doc.blocks = blocks
+  return doc
+end