Analog of the Lagrange spectrum for quadratic approximation in C
Determine whether there is a natural Lagrange-spectrum analogue governing the exponents or constants of best possible approximation of complex numbers by quadratic algebraic numbers, under the hyperbolic-distance/discriminant complexity setup developed for the complex plane.
References
There are a great many open problems motivated by this perspective. Is there a natural analog to a Lagrange spectrum?
                — An illustrated introduction to the arithmetic of Apollonian circle packings, continued fractions, and other thin orbits
                
                (2412.02050 - Stange, 3 Dec 2024) in Subsection “Open problems,” Section “Diophantine approximation in the complex plane”