  The study of twisted bilayer graphene (TBG) is a hot topic in condensed
matter physics with special focus on {\em magic angles} of twisting at which
TBG acquires unusual properties. Mathematically, topologically non-trivial flat
bands appear at those special angles. The chiral model of TBG pioneered by
Tarnopolsky--Kruchkov--Vishwanath has particularly nice mathematical properties
and we survey, and in some cases, clarify, recent rigorous results which
exploit them.
