Update textbook.fr.md

12.temporary_ins/96.electromagnetism-in-media/20.reflexion-refraction-at-interfaces/20.metallic-waveguides/10.main/textbook.fr.md

@@ -103,12 +103,15 @@ In summary, nothing changes for the
 electric or magnetic fields, but we have totally confined the
 radiation in the x and y directions.
 
+
 * For TM modes,   
-(at least for TM_m_,_0 or TM_0_,_n, see later for
+(at least for TM$`_{m\,,\,0}`$ or TM$`_{O\,,\,n}`$, see later for
 the definition of these modes), the boundary conditions cannot be
 satisfied (try to show it). In what follows we will consider for
 simplicity only the case of TE modes.
 
+
+
 @@@@@@@@@@@@@@@@@@@
 
 ![](media/image206.png)