fix: misconfigured lessons

12.temporary_ins/65.geometrical-optics/50.simple-elements/10.dioptre/20.overview/cheatsheet.en.md

@@ -5,7 +5,7 @@ published: false
 visible: false
 lessons:
    - slug: simple-optical-elements
-   - order: 1
+     order: 1
 ---
 
 !!!! *LESSON  UNDER  CONSTRUCTION :* <br>

12.temporary_ins/65.geometrical-optics/50.simple-elements/20.mirror/20.overview/cheatsheet.en.md

@@ -4,8 +4,8 @@ published: true
 routable: true
 visible: false
 lessons:
-   slug: simple-optical-elements
-   order: 2
+  - slug: simple-optical-elements
+    order: 2
 ---
 
 !!!! *LESSON  UNDER  CONSTRUCTION :* <br>

12.temporary_ins/65.geometrical-optics/50.simple-elements/30.thin-lens/20.overview/cheatsheet.en.md

@@ -6,7 +6,7 @@ routable: true
 visible: false
 lessons:
    - slug: simple-optical-elements
-   - order: 3
+     order: 3
 ---
 
 !!!! *COURS EN CONSTRUCTION :* <br>