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I don't think that it's actually formulating a bijection across the reals - the generator function looks to me to be generating the complete set of rationals.
by yarg 3y ago
I don't think that it's actually formulating a bijection across the reals - the generator function looks to me to be generating the complete set of rationals.
> Represent each real number x∈[0,1)
as a sequence of DIGITS, where each DIGIT is either in {0,…,8} or is of the form 10∗(10k−1)+i with k≥1 and i∈{0,…,8} (i.e., in {90,…,98;990,…,998;9990,…,9998;…}.
He's iterating to infinity, that sure as shit sounds countable to me.
Anyway, the conclusion that I've come to is that you can map R onto a subset of R^n such that for all values {r[1] ... r[n]} in R^n there is a value in the R -> R^n mapping within all finite bounds.
So as long as you stay away from infinitesimals (not all of them), the domains are equivalent.
https://en.wikipedia.org/wiki/Infinitesimal https://en.wikipedia.org/wiki/Infinitesimal
> In mathematics, an infinitesimal number is a quantity that is closer to zero than any standard real number, but that is not zero.
But as far as I can tell, the reverse mapping has an R^(n - 1) orthogonal that is completely unaccounted for, within those finite bounds.
(And breaking infinitesimals might cause some trouble for calculus.)
- ginnungagap 3y agoHe's associating to each x in [0,1) an infinite sequence of natural numbers (just like decimal representations do), and there's uncountably many such sequences
- yarg 3y agoBut he's defining the numbers with a property that makes them countably infinite? prefix = '0.'; queue = new Queue(prefix); for(;;){ s = queue.poll(); for(c:['0'...'9']){ queue.add(s + c); } } When the constraint is "run forever" I don't think that the generator he defined produces results any different from the snippet above.
- yarg 3y agoI may have misread that one, but I still think the reverse mapping only gets as far as within arbitrary bounds.
- yarg 3y agoThe part that seems problematic is "each real number" the reals exist across bounds, I'm not sure there can be an "each". I think his iterator is generating infinitesimals of rational and not continuous nature.