Update textbook.fr.md

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

@@ -176,7 +176,7 @@ $`\Longrightarrow`$ Existence of a cut-off frequency. The dispersion relation is
 
 We have for:
 
-* *a $`TE_{0,n}`$ mode :
+* *a $`TE_{0,n}`$ mode* :
    * if $`\omega\gt\omega_c=\dfrac{n\pi c}{b}\;\Longrightarrow\;k_z\in\mathscr{R}e`$   
      $`\Longrightarrow`$ propagation without absorption for mode $`TE_{0,n}`$.
    * if $`\omega\lt\omega_c=\dfrac{n\pi c}{b}\;\Longrightarrow\;k_z\in\mathscr{I}m`$