Michaels, Ralf MPI for Comparative and International Private Law, Max Planck Society;
https://www.bloomsburyprofessional.com/uk/multi-sourced-equivalent-norms-in-international-law-9781849461450/ (Any fulltext)
Michaels, R., & Pauwelyn, J. (2011). Conflict of Norms or Conflict of Laws?: Different Techniques in the Fragmentation of Public International Law. In T. Broude, & Y. Shany (Eds.), Multi-Sourced Equivalent Norms in International Law. Hart.