diff --git a/revealjs/alternative_energy/index.html b/revealjs/alternative_energy/index.html
index c353be0..db1c482 100644
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@@ -382,7 +382,7 @@
                 <ul>
                   <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>Encyclopedia of Science: <a href="http://www.daviddarling.info/encyclopedia/K/Kardashevciv.html">Kardashev civilzations</a></li>
+                  <li>Encyclopedia of Science: <a href="https://archive.fo/Q7Lq5">Kardashev civilzations</a><sup>✝</sup></li>
                 </ul>
               </td>
             </tr>
@@ -416,12 +416,13 @@
                   <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>Gizmodo: <a href="https://archive.fo/ZdXcc">How to build a Dyson sphere in five (relatively) easy steps</a></li>
-                  <li>Daniel Tillet: <a href="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></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>
                 </ul>
               </td>
             </tr>
           </table>
+          <small><sup>✝</sup> Archiviert vom Original</small>
           <div class="legend">
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               <li class="imageplus">Inhalts- und Bildquelle</li>