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Cake day: June 21st, 2023

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  • Where in those axioms does it say that ↑ = 0 = 0 {0 0 } is not a number? No where, that’s where!

    The actual reason that ↑ is simply that it is too ill behaved. The stuff I thought were the “numbers” of combinatorical game are actually just called Conway games. Conway numbers are defined very almost identically to Conway games, but with an added constraint that makes them a much better behaved subset of Conway games.

    I suppose you could call this an axiom of combinatorical game theory; but at that point you are essentially just calling every definition an axiom.

    <s> Getting back to my original point; this distinction just goes to show how small minded mathematicians are! Under Conway’s supposed “reasonable” definition of a number, nimbers are merely games, not proper numbers. However, the nimbers are a perfectly good infinite field of characteristic 2. You can’t seriously expect me to believe that those are not numbers! </s>


  • I was going to make a comment about surreal numbers not being numbers. But I did a bit of fact checking and it looks like all of the values I was objecting to are not considered surreal numbers, but rather pseudo numbers.

    I find this outrageous. Why can’t ↑ be a number? What even is a number that would exclude it and leave in all of your so-called numbers?



  • You get this property in algrabraic structures called “wheels”. The simplest to understand wheel is probably the wheel of fractions, which is a slightly different way of defining fractions that allows division by 0.

    The effect of this is to create 2 additional numbers: ∞ = z/0 for z != 0, ⊥, and ⊥ = 0/0.

    Just add infinity gives you the real projective line (or Riemen Sphere if you are working with comples numbers). In this structure, 0 * ∞ is undefined, so is not quite what you want

    ⊥ (bottom) in a wheel can be thought as filling in for all remaining undefined results. In particular, any operation involving ⊥ results in ⊥. This includes the identity: 0 * ⊥ = ⊥.

    As far as useful applications go, there are not many. The only time I’ve ever seen wheels come up when getting my math degree was just a mistake in defining fractions.

    In computer science however, you do see something along these lines. The most common example is floating point numbers. These numbers often include ∞, -∞ and NaN, where NaN is essentially just ⊥. In particular, 0 * NaN = NaN, also 0 * ∞ = ⊥. The main benefit here is that arithmetic operations are always defined.

    I’ve also seen an arbitrary precision fraction library that actually implemented something similar to the wheel of fractions described above (albeit with a distinction between positive and negative infinity). This would also give you 0 * ∞ = ⊥ and 0 * ⊥ = ⊥. Again, by adding ⊥ as a proper value, you could simplify the handling of some computations that might fail.