TMC21: Topological properties and Hall effects

Round-16 hunt: picked; source: course-code search, second pass at the best new universities (r16 wave 8); channel screens (sellers/exam/re-upload/devotional/vendor/events), provenance check, vendor/seller/devotional recheck and quality tier C + tier-C depth check passed; strict per-title check + final strict pass; oEmbed verified.