The realm of natural numbers | Data structures in Mathematics Math Foundations 155

[@helvitisdrasl]

I've found it useful to include a "monus" operation in Realms, which is a partial inverse of the addition operation. Particularly if I want to remove things from my multisets. I'm calling realms equipped with these m-realms (after m-semirings). The monus, if it exists, stands in a Galois-connection with the addition operator. For example, on natural numbers, it's the truncated subtraction. On the realm of multisets, it's the multiset difference function.