only recently became applicable to astrophysical simulations, very few core-collapse supernova codes are fully general relativistic at this point [@kuroda:16; @ott:13a]. The fully general-relativistic approach is much more memory and FLOP intensive than solving the Newtonian Poisson equation. Its advantage in large-scale computations, however, is the hyperbolic nature of the equations, which does not require global matrix inversions or summations and thus is advantageous for the parallel scaling of the algorithm.

-   **Neutrino Transport and Neutrino-Matter Interactions.** Neutrinos move at the speed of light (the very small neutrino masses are neglected) and can travel macroscopic distances between interactions. Therefore, they must be treated as non-equilibrium radiation. Radiation transport is closely related to kinetic theory’s Boltzmann equation. It describes the phase-space evolution of the neutrino distribution function or, in radiation transport terminology, their specific intensity. This is a 6+1 D problem: 3 spatial dimensions, neutrino energy, and two momentum space propagation angles in addition to time. The angles describe the directions from which neutrinos are coming and where they are going at a given spatial coordinate. In addition, the transport equation must be solved separately for multiple neutrino species: electron neutrinos, electron antineutrinos, and heavy-lepton ($\mu$, $\tau$) neutrinos and antineutrinos.

    Figure 