  The current measurement of muonic $g - 2$ disagrees with the theoretical
calculation by about 3 standard deviations. Hadronic vacuum polarization (HVP)
and hadronic light by light (HLbL) are the two types of processes that
contribute most to the theoretical uncertainty. The current value for HLbL is
still given by models. I will describe results from a first-principles lattice
calculation with a 139 MeV pion in a box of 5.5 fm extent. Our current
numerical strategies, including noise reduction techniques, evaluating the HLbL
amplitude at zero external momentum transfer, and important remaining
challenges, in particular those associated with finite volume effects, will be
discussed.
