So one thing one considers a lot, is taking each bin separately, and
   combining them.  I don"t know how hatd either of those are, to do.l,
   but to
   To consider whether that is reasonable to do or not, we imagine trying
   it.
   If I have one bin from a histogram, and I consider this histogram was
   sampled from a population described by another, there might be only so
   many ways of sampling the other histogram, to fill the one.