Astro2020 Science White Paper: A proposal to exploit galaxy-21cm
  synergies to shed light on the Epoch of Reionization
  This white paper highlights the crucial and urgent synergies required between
WFIRST, Subaru Hyper Suprime-Cam or other >25m-class telescopes galaxy
observations and SKA 21cm measurements to constrain the nature of reionization
(ionization history and topology) and its sources.
