brb trying to convince every graphics paper author to use the same taxonomy for implicit functions

@mjk it would actually be very useful to have a precise agreed-upon taxonomy here.

Also TIL "eikonal," much shorter than "has a Lipschitz number of 1."

@cliffle I don't think they're exactly the same – Eikonal means that the gradient is exactly 1 (or some other constant) everywhere, versus "Lipschitz continuous" means the gradient is <= 1 everywhere