Rename multiset "union" into "disjoint union"
This fixes #13 (closed). Now
∩ are the usual multiset union and intersection (i.e. taking max and min, respectively), whereas
⊎ is the "sum" (i.e. adding the multiplicities).
∪have different heights in my font (see
⊎∪). Is there maybe a better disjoint union symbol in unicode?
- There are probably all kinds of laws about the interaction between
⊎, like distributivity. I did not attempt to prove a comprehensive set of such laws.
∖is still the operation that subtracts multiplicity. I think that's fine, since there is no sensible difference operator for multisets that matches up with the union operator.