gjm comments on SciAm article about rationality corresponding only weakly with IQ - Less Wrong

5 Post author: DavidPlumpton 27 December 2014 08:56PM

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Comment author: gjm 28 December 2014 12:48:14AM 8 points [-]

I think there's a better way to think about the Jack-Anne-George problem, which generalizes more readily. You've got a chain with "married" at one end and "unmarried" at the other: so of course at some point along it there has to be a transition from the former to the latter, QED.

Comment author: buybuydandavis 30 December 2014 11:49:09PM 1 point [-]

That is a very tidy analysis.

Easier than enumerate and evaluate, but much less general.

Comment author: gjm 31 December 2014 12:12:54AM *  4 points [-]

much less general.

It instantly gives you the answer to cases that look like A->B->C->D->...->Z where enumerate-and-evaluate requires you to consider 2^24 possibilities.

Let's think a moment about further generalization. So you have an arbitrary directed graph where a->b means a is looking at b; some vertices are coloured white ("married") and some black ("unmarried"), and the question is: is there a way to colour all the vertices black and white that has no instance of white->black?

Well, if there is any chain of arrows starting at a white vertex and ending with a black one, then the reasoning I described tells you that in any colouring there must be a white->black edge.

On the other hand, if there isn't then we can start at every white vertex, walking along arrows and whitening every vertex we reach; since there is no W->...->B chain this will never produce a clash. At this point we have whitened every vertex reachable from a white one, so now we can colour all the rest black; we've coloured the whole graph without any W->B edges.

So we have our (maximally generalized) answer: the answer to "must a married person be looking at an unmarried person?" is "yes, if there is a married->...->unmarried chain somewhere; no, otherwise". And (so it seems to me) this is just following the path of least resistance using the approach I described. So I'm going to stand by my claim that it "generalizes more readily".

Comment author: solipsist 29 December 2014 05:09:30AM -1 points [-]

Assuming the only states are married and unmarried. I'm not sure if I would call a widow unmarried, in the same way I'm not sure if I would call a man with a surgically reattached foreskin uncircumcised.

Comment author: gjm 29 December 2014 03:08:35PM 3 points [-]

Sure. (I think it's pretty obvious in the "puzzle" context that you're supposed to take "married" and "unmarried" as exhausting the possibilities, though.)

Comment author: buybuydandavis 30 December 2014 09:16:07PM *  1 point [-]

I'd call a widow unmarried if she wasn't currently married.

I suppose the language usage might get complicated.

Is she still a widow, in the present tense, after she has remarried? Looking at a few definitions, it appears so, but the archtype of widow is one who has yet to remarry.

Comment author: ChristianKl 30 December 2014 10:52:53PM 0 points [-]

Marriages vows are "Till Death Do Us Part".