Ellipses and compositions of finite Blaschke products
Journal of Mathematical Analysis and Applications
We provide a new proof of a theorem of Fujimura characterizing Blaschke products of degree-4 that are compositions of two degree-2 Blaschke products, connect this result to the numerical ranges of certain operators, and characterize Poncelet ellipses that are inscribed in quadrilaterals geometrically and algebraically.
Gorkin, Pamela and Wagner, Nathan. "Ellipses and compositions of finite Blaschke products." Journal of Mathematical Analysis and Applications 445, no. 2 (2017) : 1354-1366.