Siehr, Kurt MPI for Comparative and International Private Law, Max Planck Society;
https://kluwerlawonline.com/journalarticle/European+Review+of+Private+Law/28.3/ERPL2020028 (Any fulltext)
Max Planck Private Law Research Paper No. 21/4 (Any fulltext)
Siehr, K. (2020). Mandatory Rules of Third States From Ole Lando to Contemporary European Private International. European Review of Private Law, 28, 509-522.