Sample a known histogram of a population.
   Say there nbuckets bins, and poptotal events.
   When we sample a histogram, I think there are ... Some number of total
   ways to do it.  The poptotal.  So there are poptotal total options for
   the first sample and poptotal^samptotal total sampled histograms: and
   many of those histograms are identical, indicating they are more
   probable.
   I am definitely making a number of weighted choices repeatedly.