Update cheatsheet.en.md

12.temporary_ins/69.waves/10.n1/20.overview/cheatsheet.en.md

@@ -52,4 +52,15 @@ $`\def\PSclosed{\mathscr{S}_{\displaystyle\tiny\bigcirc}}`$
 
 <img src="https://m3p2.com/fr/temporary_ins/waves/n1/overview/sillage-a_v3_L900.gif" alt="Description du GIF" style="width:100%; height:auto;" />
 
+!! <details markdown=1><summary>To go further</summary>
+!!
+!! ![](https://m3p2.com/fr/temporary_ins/waves/n2/overview/waves-doppler-immob_1ok_L900.gif)
+!!
+!! ![](https://m3p2.com/fr/temporary_ins/waves/n2/overview/wave-doppler-subsonic_L900.gif)
+!!
+!! ![](https://m3p2.com/fr/temporary_ins/waves/n2/overview/doppler-moving-source-mach1-v2_L900.gif)
+!!
+!! ![](https://m3p2.com/fr/temporary_ins/waves/n2/overview/mechanical-waves-doppler-hypersonic_L900.gif)
+!! </details>
+
 ![](interference-diffraction-waves-television_L1200.jpg)