diff --git a/revealjs/alternative_energy/index.html b/revealjs/alternative_energy/index.html
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--- a/revealjs/alternative_energy/index.html
+++ b/revealjs/alternative_energy/index.html
@@ -411,8 +411,8 @@
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-                  <li class="image"><a href="https://500px.com/photo/106595393">500px/Jan Bambach</a> <a href="https://creativecommons.org/licenses/by-sa/3.0/deed.en">CC-BY-SA 3.0</a></li>
-                  <li class="image">YouTube/Kurzgesagt (<a href="https://youtu.be/wWSJYr1Lr0E">wWSJYr1Lr0E</a>)</li>
+                  <li class="image">500px: <a href="https://500px.com/photo/106595393">Jan Bambach</a> <a href="https://creativecommons.org/licenses/by-sa/3.0/deed.en">CC-BY-SA 3.0</a></li>
+                  <li class="image">YouTube: <a href="https://www.youtube.com/channel/UCwRH985XgMYXQ6NxXDo8npw">Kurzgesagt (de)</a> (<a href="https://youtu.be/wWSJYr1Lr0E">wWSJYr1Lr0E</a>)</li>
                   <li>Encyclopedia of Science: <a href="https://archive.fo/Q7Lq5">Kardashev civilzations</a><sup>✝</sup></li>
                 </ul>
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@@ -420,16 +420,16 @@
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-                  <li class="image">Unsplash/<a href="https://unsplash.com/photos/vCqclUnCg_8">Frank Denney</a></li>
-                  <li class="image"><a href="https://de.wikipedia.org/wiki/Datei:Geothermie_verfahren.png">Geothermie verfahren.png</a>: Jkrieger Public Domain (angepasst)</li>
-                  <li>Wikipedia (de): <a href="https://de.wikipedia.org/wiki/Geothermie">Geothermie</a></li>
+                  <li class="image">Unsplash: <a href="https://unsplash.com/photos/vCqclUnCg_8">Frank Denney</a></li>
+                  <li class="image">Wikimedia Commons: <a href="https://de.wikipedia.org/wiki/Datei:Geothermie_verfahren.png">Geothermie verfahren.png</a>: <a href="https://de.wikipedia.org/wiki/user:Jkrieger">Jkrieger</a> Public Domain (angepasst)</li>
+                  <li>Wikipedia (de): <a href="https://archive.fo/ibom7">Geothermie</a><sup>✝</sup></li>
                 </ul>
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-                  <li class="image"><a href="https://commons.wikimedia.org/wiki/File:Biogas.jpg">Biogas.jpg</a>: Volker Thies <a href="https://creativecommons.org/licenses/by-sa/3.0/deed.en">CC-BY-SA 3.0</a></li>
+                  <li class="image">Wikimedia Commons: <a href="https://commons.wikimedia.org/wiki/File:Biogas.jpg">Biogas.jpg</a>: <a href="https://commons.wikimedia.org/wiki/User:Asdrubal">Volker Thies</a> <a href="https://creativecommons.org/licenses/by-sa/3.0/deed.en">CC-BY-SA 3.0</a></li>
                   <li>…</li>
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@@ -445,9 +445,8 @@
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-                  <li class="image">YouTube/Kurzgesagt (<a href="https://youtu.be/wWSJYr1Lr0E">wWSJYr1Lr0E</a>)</li>
-                  <li class="imageplus">YouTube/Kurzgesagt (<a href="https://youtu.be/ulCdoCfw-bY">ulCdoCfw-bY</a>)</li>
-                  <!--<li>Arχive.org: <a href="https://arxiv.org/abs/1112.5519">1112.5519 [physics.gen-ph]</a></li>-->
+                  <li class="image">YouTube: <a href="https://www.youtube.com/channel/UCwRH985XgMYXQ6NxXDo8npw">Kurzgesagt (de)</a> (<a href="https://youtu.be/wWSJYr1Lr0E">wWSJYr1Lr0E</a>)</li>
+                  <li class="imageplus">YouTube: <a href="https://www.youtube.com/channel/UCsXVk37bltHxD1rDPwtNM8Q">Kurzgesagt (en)</a> (<a href="https://youtu.be/ulCdoCfw-bY">ulCdoCfw-bY</a>)</li>
                   <li>Gizmodo: <a href="https://archive.fo/ZdXcc">How to build a Dyson sphere in five (relatively) easy steps</a><sup>✝</sup></li>
                   <li>Daniel Tillet: <a href="https://web.archive.org/web/20170610111407/https://www.tillett.info/2016/08/03/carnot-efficient-dyson-spheres-are-undetectable-by-infrared-surveys/">Carnot Efficient Dyson Spheres are Undetectable by Infrared Surveys</a><sup>✝</sup></li>
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