Subtract axial distributions, finding the difference (under an additive variance framework).
This is most useful when one distribution subsumes another and includes a unique dispersal event that needs to be extracted.
For example, the FS category is subsumed by the 1C category, which can be written 'FS + PO'.
In this circumstance, subtracting FS from 1C will yield an estimate of the PO kernel (the basic intergenerational dispersal kernel)