def METHOD_NAME(self, ispan, ospan):
    idata, odata = ispan.data, ospan.data
    bf_reduce(idata, odata, self.op)
    # TODO: Support system space using Numpy
    #ishape = list(idata.shape)
    #ishape[self.axis] //= self.factor
    #ishape.insert(self.axis+1, self.factor)