Manfred comments on Draft/wiki: Infinities and measuring infinite sets: A quick reference - Less Wrong

27 Post author: Sniffnoy 24 December 2010 04:52AM

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Comment author: Manfred 24 December 2010 05:41:09AM 1 point [-]

Blorst horst.

I would like it if you paired each "myth" line with an explicit "truth" line that gave the tl;dr for us, maybe even using simple language e.g.

Myth: The cardinalities of infinite sets can be compared like ordinary numbers. Reality: If the axiom of choice is false, you can have one set's cardinality be both larger and smaller than another's

(maybe even a short blurb explaining the axiom of choice's role)

I could still understand you, but it certainly helped that I'd borrowed my friend's topology book over the summer.

Rather than making a big list, some more structure and an actual conclusion to topic #1 would have helped cement things in my brain.

Since this turned out pretty long, you could actually split the topics into separate posts in a series. And with a little editing I would be all for these being top-level posts rather than discussion secion.

Comment author: Eugine_Nier 24 December 2010 06:00:46AM 4 points [-]

Reality: If the axiom of choice is false, you can have one set's cardinality be both larger and smaller than another's

Actually without the axiom of choice, one set's cardinality can be neither larger nor smaller than another's.

Comment author: Sniffnoy 24 December 2010 06:12:40AM 1 point [-]

Blorst horst.

OK, I have to ask, how exactly did that become visible?

I would like it if you paired each "myth" line with an explicit "truth" line that gave the tl;dr for us, maybe even using simple language e.g.

Myth: The cardinalities of infinite sets can be compared like ordinary numbers. Reality: If the axiom of choice is false, you can have one set's cardinality be both larger and smaller than another's

Ah, this is a good idea, especially because the correction you propose is not quite correct. :) It would be neither larger nor smaller. I see I made the mistake there of assuming familiarity with partial orders, which was foolish; I forgot people need to be explicitly introduced to those.

(maybe even a short blurb explaining the axiom of choice's role)

Hm, do you really think that would help? I was trying to more of provide a quick reference of facts, while referring elsewhere for proofs.

Comment author: Manfred 24 December 2010 08:27:08PM *  1 point [-]

Blorst horst.

OK, I have to ask, how exactly did that become visible?

Magic. Also, you might have pressed a button.

(maybe even a short blurb explaining the axiom of choice's role)

Hm, do you really think that would help? I was trying to more of provide a quick reference of facts, while referring elsewhere for proofs.

You can still do that to a large degree, but I think that even for a LW audience it would be helpful to say what it is, state that it was used in the proof, and explain briefly why we should keep both axiom-of-choice-is-true and axiom-of-choice-is-false cases in mind.

Comment author: Sniffnoy 25 December 2010 02:47:19AM 0 points [-]

Magic. Also, you might have pressed a button.

What I mean is, did you see it when I accidentally posted it the first time, before I deleted it, or did you somehow see it after I then deleted it (in which case my name would have appeared as "[deleted]"), or were you somehow able to find the old version after I posted the new one?

Comment author: Manfred 25 December 2010 06:05:46AM 0 points [-]

Saw it the first time, composed first draft of comment then, tried to post and found out it had been deleted, was sad.

Comment author: rhollerith_dot_com 24 December 2010 04:50:14PM 0 points [-]

I would like it if you paired each "myth" line with an explicit "truth" line that gave the tl;dr for us, maybe even using simple language

I would have gone the other way and abandoned the attempt to arrange things in a list. I.e., I would have made the structure simpler, e.g., sections divided into paragraphs, e.g., no attempt to number anything.