Textbook Edit

Writing rules

Content structure

• Each chapter follows: motivation → intuition → math → worked example → implementation notes
• Sections within a chapter: opening question → ELI5 → formal treatment → summary box
• Comparison tables for any "A vs B" discussion (e.g., FEM vs FDM, Strang vs Godunov)

Equations

• Numbering: Chapter N uses equations (N.1), (N.2), etc. Check INDEX.md equation registry for the last used number.
• Never orphan an equation — every equation must have a plain-English sentence before it explaining what it means and a sentence after explaining what to notice
• Use underbrace for annotating terms in key equations
• Check for conflicts after adding new equations — renumber if needed

Cross-references

• Reference other chapters by number: "as we saw in Chapter 7..."
• Reference equations by number: "from equation (12.3)..."
• When citing research, use the citation key from Research/INDEX.md and note the paper title inline

Editing large sections

For replacements larger than 50 lines:

1. Write the new content to a temporary file (e.g., /tmp/chapter_12_section_3.html)
2. Use a Python splice script to replace the line range:

# Read original, splice in new content, write back
lines = open('Bidomain_Textbook.html').readlines()
new_content = open('/tmp/chapter_12_section_3.html').readlines()
lines[start:end] = new_content
open('Bidomain_Textbook.html', 'w').writelines(lines)

3. This avoids Edit tool failures on large non-unique blocks

After editing

1. Update CHANGELOG.md — add a dated entry describing what changed, design decisions made, and any issues resolved
2. Update INDEX.md — if line numbers shifted, update the chapter line ranges. If equations were added/renumbered, update the equation registry.
3. Compile the PDF — use /textbook-compile to build and verify