[1] are the exercises with solutions (!) of a lecture [2] at ETH Zurich, which include AVL trees in Isabel. The whole list of exercise PDFs is at [3]. I started porting the AVL trees to Scheme [4], but lately have not worked more on this. I also try to make it easy to understand the implementation by providing explanatory comments.
[1]: https://archiv.infsec.ethz.ch/education/permanent/csmr/exerc...
[2]: https://archiv.infsec.ethz.ch/education/permanent/csmr.html
[3]: https://archiv.infsec.ethz.ch/education/permanent/csmr/exerc...
[4]: https://codeberg.org/ZelphirKaltstahl/guile-data-structures/...