I haven't seen this discussed here yet, but a month ago a Mexican physicist apparently found an analytic solution to the Wasserman-Wolf problem, i.e. the solution to eliminating spherical aberration in a singlet:
https://petapixel.com/2019/07/05/goo...tical-problem/
This will be great news for makers of small and flat photographic lenses (smartphones!) and lenses used anywhere the remaining aberrations (mostly chromatic, AMD) can be computationally reduced. Refractors for visual observation will need a bit extra effort still.
