Update textbook.en.md

12.temporary_ins/05.coordinates-systems/30.cylindrical-coordinates/10.main/textbook.en.md

@@ -9,8 +9,6 @@ lessons:
     - slug: cylindrical-coordinates-linear
       order: 1
 ---
-
-
 <!--caligraphie de l'intégrale double curviligne-->
 $`\def\oiint{\displaystyle\mathop{{\iint}\mkern-18mu \scriptsize \bigcirc}}`$
 $`\def\Ltau{\Large{\tau}\normalsize}`$
@@ -24,6 +22,8 @@ $`\def\PSclosed{\mathscr{S}_{\displaystyle\tiny\bigcirc}}`$
 !!!! Published but invisible: does not appear in the tree structure of the m3p2.com site. This course is *under construction*, it is *not approved by the pedagogical team* at this stage. <br>
 !!!! Working document intended only for the pedagogical team.
 
+-------------------------
+
 <!--MétaDonnée : INS-1°année_-->
 
 ! *Suggested method:*