Replace a broken YouTube link

src/mir/dataflow.md

@@ -18,7 +18,8 @@ If you're unfamiliar with these terms, or if you want a quick refresher,
 [*Static Program Analysis*] by Anders Møller and Michael I. Schwartzbach is an
 excellent, freely available textbook. For those who prefer audiovisual
 learning, the Goethe University Frankfurt has published a series of short
-[lectures on YouTube][goethe] in English that are very approachable.
+[lectures on YouTube][goethe] in English that are very approachable (NOTE: the creator
+removed their content from YouTube. For now, we provide a link to the Wayback Machine).
 
 ## Defining a Dataflow Analysis
 
@@ -229,6 +230,6 @@ the example below:
 [`apply_call_return_effect`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_mir_dataflow/trait.Analysis.html#tymethod.apply_call_return_effect
 [`into_engine`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_mir_dataflow/trait.Analysis.html#method.into_engine
 [`lattice`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_mir_dataflow/lattice/index.html
-[goethe]: https://www.youtube.com/watch?v=NVBQSR_HdL0&list=PL_sGR8T76Y58l3Gck3ZwIIHLWEmXrOLV_&index=2
+[goethe]: https://web.archive.org/web/20200221205557/https://www.youtube.com/watch?v=NVBQSR_HdL0
 [lattice]: https://en.wikipedia.org/wiki/Lattice_(order)
 [wiki]: https://en.wikipedia.org/wiki/Data-flow_analysis#Basic_principles