Thanks for your insights, @offer! One of these days I'll delve more into Lie algebras, projective spaces, and kernels. Right now I'm a bit more interested in the stuff I mentioned in Parts 3 to 5. I have a lot of questions about them, but I'll just share a couple here.
1. Matrix representations
I really want to know what the deal is with the matrix representations of polytopic algebras. I mean, it would have been so cool if they're just always circulant. There's a whole Wikipedia article about circulant matrices, and they are fascinating. But no, for an even number of dimensions we get this instead (taken from Part 4):
Does this specific kind of matrix even have a name? Wolfram Alpha only describes it as both normal and Toeplitz, which is well and good, but those descriptions also apply to circulant matrices. What do we make of these Toeplitz matrices that are almost circulant but whose entries above the main diagonal are the additive inverses of the ones below? Skew-symmetric Toeplitz matrices are just a small subset of these, but then there's not a lot about those, either.
And yet, the 2x2 matrix representation of complex numbers are of this form. The only reason I discovered the above matrix form in the first place is because the complex numbers are the motivating example for the even cases of Xn, and so I just tried to generalize its matrix form. I just wish I could read more about this Toeplitz variant, particularly its relationship to circulant matrices.
2. The Addition Problem
For multirationals, including fractions and trirationals, addition is more complicated than multiplication. And as you move towards higher multirationals, it gets way more complicated way fast. One motivation for constructing the polytopic algebras is that since we can create multirationals in them, we can theoretically convert two such multirationals to the algebra's Cartesian form, add them together (term-wise addition FTW!), then convert them back to a multirational. Theoretically.
I mean, at least I was able to do it for complex numbers, right? The section on trirational addition in Part 2 is probably my favorite section of the whole series. Alas, I'm finding it very challenging to repeat this process for the next polytopic algebra after the complex numbers, which we can call X3 or triplex. I feel that it must be doable with enough mathematical skill. After all, I already know how to make 4-rational numbers in X3 (using the process I explained in Part 5). I also know the exponential formula for X3 so I can actually evaluate 4-rationals to get the Cartesian form. But I have no idea how to convert the X3 Cartesian form to 4-rational form. Do you have any tips on how to do this?
(If you're wondering, I was able to do this for complex numbers because I spent months playing around with trirationals in Wolfram Alpha until I one day had a spark of intuition. I don't think I can do the same thing for algebras that Wolfram Alpha doesn't support.)