Rework the tree structure again.

This is verbose but very powerful.

fr/01.optique/03.la-nature-de-la-lumiere/cahier.md → fr/01.optique/03.la-nature-de-la-lumiere/01.cahier/textbook.md

 ---
 title: "La nature de la lumière"
 dependencies:
-  - optics/chapter2
+  - fr/optique/???
 ---
 
 <!--

fr/01.optique/03.la-nature-de-la-lumiere/02.antiseche/cheatsheet.md

+## Trucs & Astuces
+
+Lorem ipsum…
\ No newline at end of file

fr/01.optique/03.la-nature-de-la-lumiere/columns.md

+---
+content:
+    # https://learn.getgrav.org/15/content/collections#summary-of-collection-options
+    items: @self.children
+---
\ No newline at end of file

fr/01.optique/topic.md

+---
+content:
+    # https://learn.getgrav.org/15/content/collections#summary-of-collection-options
+    items: @self.children
+---
\ No newline at end of file

fr/topics.md

+---
+content:
+    # https://learn.getgrav.org/15/content/collections#summary-of-collection-options
+    items: @self.children
+---
\ No newline at end of file