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penteract commented on Making geo joins faster with H3 indexes   floedb.ai/blog/how-we-mad... · Posted by u/matheusalmeida
anacoluthe · a day ago
Beware that the parent hexagon does not contain its children...
penteract · a day ago
No idea if they are doing this, but you can use Gosper islands (https://en.wikipedia.org/wiki/Gosper_curve) which are close to hexagons, but can be exactly decomposed into 7 smaller copies.
penteract commented on Typechecking is undecidable when 'type' is a type (1989) [pdf]   dspace.mit.edu/bitstream/... · Posted by u/zem
kingstnap · 6 days ago
I'm not entirely smart enough to connect all of these things together but I think there is a kind of subtlety here thats being stepped on.

1. Complete, Decidable, Well founded are all distinct things.

2. Zig (which allows types to be types) is Turing complete at compile time regardless. So the compiler isn't guaranteed to halt regardless and it doesn't practically matter.

3. The existance of a set x contains x is not enough by itself to create a paradox and prove false. All it does is violate the axiom of foundation, not create a russles paradox.

4. The axiom of foundation is a weird sort of arbitrariness in that it implies this sort of DAG nature to all sets under set membership operation.

5. This isn't nessesarily some axiomatically self evident fact. Aczel's anti foundation axiom works as well and you can make arbitrary sets with weird memberships if you adopt that. https://en.wikipedia.org/wiki/Aczel%27s_anti-foundation_axio...

6. The Axiom of Foundation exists to stop you from making weird cycles, but there is parallel to the axiom of choice, which directly asserts the existance of non computable sets using a non algorithmicly realizable oracle anyway....

penteract · 6 days ago
Your other points are more relevant to the content of the article, but point 2. relates the practical consequences of undecidable type-checking, so I'll reply to that.

I don't have a problem with compile time code execution potentially not terminating, since it's clear to the programmer why that may happen. However, conventional type checking/inference is more like solving a system of constraints, and the programmer should understand what the constraints mean, but not need to know how the constraint solver (type checker) operates. If it's undecidable, that means there is a program that a programmer knows should type check, but the implementation won't be happy with; ruining the programmer's blissful ignorance of the internals.

penteract commented on Typechecking is undecidable when 'type' is a type (1989) [pdf]   dspace.mit.edu/bitstream/... · Posted by u/zem
pvillano · 7 days ago
This stack exchange answer talks about the importance of decidability in type checking

https://langdev.stackexchange.com/a/2072

My interpretation

Decidability is of academic interest, and might be a hint if something is feasible.

But there are (1) ways of sidestepping undecidability, e.g. A valid C++/Rust program is one for which the typechecker terminates in x steps without overflowing the stack

And (2) things which are decidable, but physically impossible to calculate, e.g the last digit of the 10^10^10 th prime

What matters is being able to reject all incorrect programs, and accept most human written valid programs

penteract · 6 days ago
Decidability of a type system is like well-typedness of a program. It doesn't guarantee it's sensible, but not having the property is an indicator of problems.
penteract commented on Typechecking is undecidable when 'type' is a type (1989) [pdf]   dspace.mit.edu/bitstream/... · Posted by u/zem
jeberle · 7 days ago
Does Rice's theorem cover this?

> [ all non-trivial semantic properties of programs are undecidable ]

https://en.wikipedia.org/wiki/Rice's_theorem

Found here:

From Sumatra to Panama, from Babylon to Valhalla

https://www.youtube.com/watch?v=bE1bRbZzQ_k&t=48m27s

penteract · 6 days ago
No. Being well typed is not a semantic property of of a program - in a language where it makes sense to talk about running badly typed code, a piece of code that starts with an infinite loop may be well or badly typed after that point with no observable difference in program behaviour.

There are decidable type systems for Turing complete languages (many try to have this property), and there are languages in which all well typed programs terminate for which type checking is undecidable (System F without all type annotations).

Deleted Comment

penteract commented on Six-decade math puzzle solved by Korean mathematician   koreaherald.com/article/1... · Posted by u/mikhael
cousin_it · a month ago
I love the kind of science reporting on display in this article! It stays at a consistent, objective level of detail throughout (no "imagine a vector space as a block of jello" or whatever it is that Quanta and other publications are always doing). It allows specialists to understand exactly what's being claimed, and at the same time stays accessible to laypeople. It feels like it's written for the kind of reader that I aspire to be: not necessarily a specialist on every topic under the sun, but someone who has finished high school and is paying attention.

Though I guess writing like this doesn't pay off in the modern world. Most readers don't consistently pay attention when reading, and to be honest, I don't either.

penteract · a month ago
For many publications you could be critisizing, I'd agree with you, but Quanta usually reaches a higher standard that I feel they deserve credit for. Here's the Quanta article on the same thing [1]. It goes into much more detail, it shows a picture of the perfect sofa, and links to the actual research paper. They're aimed at a level above "finished high school", and I appreciate that; it gives me a chance to learn from the solution to a problem, and encourages me to think about it independently.

I agree with you that Quanta doesn't always "allow specialists to understand exactly what's being claimed", which is a problem; but linking to the research papers greatly mitigates that sin.

[1] https://www.quantamagazine.org/the-largest-sofa-you-can-move...

And here's how they clearly explain the proof strategy.

> First, he showed that for any sofa in his space, the output of Q would be at least as big as the sofa’s area. It essentially measured the area of a shape that contained the sofa. That meant that if Baek could find the maximum value of Q, it would give him a good upper bound on the area of the optimal sofa.

> This alone wasn’t enough to resolve the moving sofa problem. But Baek also defined Q so that for Gerver’s sofa, the function didn’t just give an upper bound. Its output was exactly equal to the sofa’s area. Baek therefore just had to prove that Q hit its maximum value when its input was Gerver’s sofa. That would mean that Gerver’s sofa had the biggest area of all the potential sofas, making it the solution to the moving sofa problem.

penteract commented on Show HN: I made a spreadsheet where formulas also update backwards   victorpoughon.github.io/b... · Posted by u/fouronnes3
penteract · 2 months ago
This is great.

Since you've asked about bugs, I tried pushing the limits and found the following:

    A1: 100          B1: =100-A1
    A2: =A1*(100-A1)
    A3: =A1*B1
A2 can be successfully set to anything reasonable (up to 2500)

However, setting A3 to exactly 100 doesn't work, even though setting it to 101 or 99 (or even 100.000001) does work.

Another limit:

    A1: 100          B1: 100
    A2: =A1+B1
    A3: =A1*B1
    A4: =abs(A2-100) + abs(A3-100)
Setting A4 to zero (or anything below 80) doesn't work. This doesn't improve if the constants in the A4 formula are moved a short distance away from 100.

In case you can't tell from that last example, I think being able to fix the intended values of multiple outputs simultaneously would be interesting. If you were to give more details about the solver's internals, I'd be keen to hear them.

penteract commented on Using secondary school maths to demystify AI   raspberrypi.org/blog/seco... · Posted by u/zdw
phantasmish · 2 months ago
The simulation isn't an operating brain. It's a description of one. What it "means" is imposed by us, what it actually is, is a shitload of graphite marks on paper or relays flipping around or rocks on sand or (pick your medium).

An arbitrarily-perfect simulation of a burning candle will never, ever melt wax.

An LLM is always a description. An LLM operating on a computer is identical to a description of it operating on paper (if much faster).

penteract · 2 months ago
I believe that the important part of a brain is the computation it's carrying out. I would call this computation thinking and say it's responsible for consciousness. I think we agree that this computation would be identical if it were simulated on a computer or paper. If you pushed me on what exactly it means for a computation to physically happen and create consciousness, I would have to move to statements I'd call dubious conjectures rather than beliefs - your points in other threads about relying on interpretation have made me think more carefully about this.

Thanks for stating your views clearly. I have some questions to try and understand them better:

Would you say you're sure that you aren't in a simulation while acknowledging that a simulated version of you would say the same?

What do you think happens to someone whose neurons get replaced by small computers one by one (if you're happy to assume for the sake of argument that such a thing is possible without changing the person's behavior)?

penteract commented on What's the deal with Euler's identity?   lcamtuf.substack.com/p/wh... · Posted by u/surprisetalk
xeonmc · 2 months ago
Never liked that form of the Euler's formula. I prefer the following:

    (-1)ˣ = cos(πx) + i sin(πx)

penteract · 2 months ago
My objection to that is that there isn't a particularly natural reason not to say

       (-1)ˣ = cos(πx) - i sin(πx)
As a formula about e^iπx, there is no such conflict.

penteract commented on “Boobs check” – Technique to verify if sites behind CDN are hosted in Iran   twitter.com/hkashfi/statu... · Posted by u/defly
dhab · 2 months ago
Could someone help me understand. I looked at: https://developers.cloudflare.com/ssl/origin-configuration/s... it seems to support multiple modes.

I didn't quite get if Automatic TLS (https://developers.cloudflare.com/ssl/origin-configuration/s...) could use plain transfers.

So:

* Is it insecure by default or you have to be intentionally insecure?

* Why would anyone pick the flexible/potentially-insecure option?

penteract · 2 months ago
> Why would anyone pick the flexible/potentially-insecure option?

Because having a connection that's encrypted between a user and Cloudflare, then unencrypted between Cloudflare and your server is often better than unencrypted all the way. Sketchy ISPs could insert/replace ads, and anyone hosting a free wifi hotspot could learn things your users wouldn't want them to know (e.g. their address if they order a delivery).

Setting up TLS properly on your server is harder than using Cloudflare (disclaimer: I have not used Cloudflare, though I have sorted out a certificate for an https server).

The problem is that users can't tell if their connection is encrypted all the way to your server. Visiting an https url might lead someone to assume that no-one can eavesdrop on their connection by tapping a cross-ocean cable (TLS can deliver this property). Cloudflare breaks that assumption.

Cloudflare's marketing on this is deceptive: https://www.cloudflare.com/application-services/products/ssl... says "TLS ensures data passing between users and servers is encrypted". This is true, but the servers it's talking about are Cloudflare's, not the website owner's.

Going through to "compare plans", the description of "Universal SSL Certificate" says "If you do not currently use SSL, Cloudflare can provide you with SSL capabilities — no configuration required." This could mislead users and server operators into thinking that they are more secure than they actually are. You cannot get the full benefits of TLS without a private key on your web server.

Despite this, I would guess that Cloudflare's "encryption remover" improves security compared to a world where Cloudflare did not offer this. I might feel differently about this if I knew more about people who interact with traffic between Cloudflare's servers and the servers of Cloudflare's customers.

u/penteract

KarmaCake day576May 7, 2019View Original