diff --git a/00.brainstorming-pedagogical-teams/general/textbook.en.md b/00.brainstorming-pedagogical-teams/general/textbook.en.md
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--- a/00.brainstorming-pedagogical-teams/general/textbook.en.md
+++ b/00.brainstorming-pedagogical-teams/general/textbook.en.md
@@ -25,4 +25,18 @@ to a correct translation (from the original proposal and the automatic translati
 2 * Beware of punctuation
 -------------------------
 The internet browsers read texts correctly in the language chosen for the
-computer operating system, but the quality of autoplay depends on punctuation.
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+computer operating system, but the quality of autoplay depends on punctuation.
+
+3 * Pedagogy
+-------------
+* Do not think "course at level 3", but think "pedagogical path on levels 1 to 4".<br>
+You do not work at level 3, recalling (too) quickly the useful background
+(essential but often poorly mastered by students) required to understand your course.
+Your course must be designed with the 4 levels in mind. Structure the difficulties
+and prerequisites of your teaching in levels, and work in parallel on
+the 4 levels. Structure in levels means, for each level N: <br>
+\- what is the added value of that level N, which provides new concepts and mathematical 
+toolsn that open new horizons in the thematic?<br>
+\- which vision and basic notions must remain at lower levels of complexity and
+mastering?
+\- what should I reserve for the upper level(s)?
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