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2-category 2-category-theory abelian-categories adjoint algebra algebraic algebraic-geometry algebraic-topology analysis analytic-geometry arithmetic arithmetic-geometry book bundles calculus categorical categories category category-theory chern-weil-theory cohesion cohesive-homotopy-type-theory cohomology colimits combinatorics complex complex-geometry computable-mathematics computer-science constructive cosmology definitions deformation-theory descent diagrams differential differential-cohomology differential-equations differential-geometry digraphs duality elliptic-cohomology enriched fibration foundation foundations functional-analysis functor gauge-theory gebra geometric-quantization geometry graph graphs gravity grothendieck group group-theory harmonic-analysis higher higher-algebra higher-category-theory higher-differential-geometry higher-geometry higher-lie-theory higher-topos-theory homological homological-algebra homotopy homotopy-theory homotopy-type-theory index-theory integration integration-theory k-theory lie-theory limits linear linear-algebra locale localization logic mathematics measure-theory modal modal-logic model model-category-theory monad monads monoidal monoidal-category-theory morphism motives motivic-cohomology nlab noncommutative noncommutative-geometry number-theory object of operads operator operator-algebra order-theory pages pasting philosophy physics pro-object probability probability-theory quantization quantum quantum-field quantum-field-theory quantum-mechanics quantum-physics quantum-theory question representation representation-theory riemannian-geometry scheme schemes set set-theory sheaf simplicial space spin-geometry stable-homotopy-theory stack string string-theory superalgebra supergeometry svg symplectic-geometry synthetic-differential-geometry terminology theory topology topos topos-theory tqft type type-theory universal variational-calculus

1. • CommentRowNumber1.
   • CommentAuthorUrs
   • CommentTimeMay 3rd 2011
   • (edited May 3rd 2011)
   • PermaLink
   Author: Urs
   Format: MarkdownItexAnyone who from time to time posts messages here whose creation costs more than a few minutes will know it: the reCaptcha quiz that the nForum software requires you to solve in order to prove that you are not a robot. Every now and then, there is a letter in the Quiz that I just simply cannot decipher. Is that little hook an "r" or a "c"? So far I always was always lucky and guessed right and was never accused of being a robot. But I find it slightly annoying. But now, a minute ago I was rather baffled: the symbols that I was asked to recognize started wite "$a \in \Sigma$". How am I to know what the right answer is supposed to be? Maybe a e S or $ a \in \Sigma $ or [latex a \in \Sigma] or a \in \Sigma ?? I went for the latter -- and was lucky once again. I hope my luck will not fail me in the future.

   Anyone who from time to time posts messages here whose creation costs more than a few minutes will know it: the reCaptcha quiz that the nForum software requires you to solve in order to prove that you are not a robot.

   Every now and then, there is a letter in the Quiz that I just simply cannot decipher. Is that little hook an “r” or a “c”? So far I always was always lucky and guessed right and was never accused of being a robot. But I find it slightly annoying.

   But now, a minute ago I was rather baffled: the symbols that I was asked to recognize started wite “$a \in \Sigma$”.

   How am I to know what the right answer is supposed to be?

   Maybe

     a e S
   

   or

   $ a \in \Sigma $
   

   or

   [latex a \in \Sigma]
   

   or

   a \in \Sigma
   

   ??

   I went for the latter – and was lucky once again. I hope my luck will not fail me in the future.

2. • CommentRowNumber2.
   • CommentAuthorUrs
   • CommentTimeMay 3rd 2011
   • PermaLink
   Author: Urs
   Format: MarkdownItexOh. Only now have I looked at <a href="http://www.google.com/recaptcha/learnmore">their website</a>. Okay, now I am all in favor of this. And now I also understand why genuinely unreadable characters and why mathematical symbols can show up. And why in the cases that I thought I was lucky, on the contrary I wasn't being tested but was asked for an opinion. ;-)

   Oh.

   Only now have I looked at their website.

   Okay, now I am all in favor of this. And now I also understand why genuinely unreadable characters and why mathematical symbols can show up. And why in the cases that I thought I was lucky, on the contrary I wasn’t being tested but was asked for an opinion. ;-)

3. • CommentRowNumber3.
   • CommentAuthorAndrew Stacey
   • CommentTimeMay 3rd 2011
   • PermaLink
   Author: Andrew Stacey
   Format: MarkdownItexI'd seen these (that is, the mathematical ones) on MathOverflow but hadn't thought about their impact here. I should make the "reload" button work properly so that if someone gets a recaptcha that they really can't solve, they can click on the "reload" to get a new one. And, no, I have no idea what you are supposed to type for mathematics.

   I’d seen these (that is, the mathematical ones) on MathOverflow but hadn’t thought about their impact here. I should make the “reload” button work properly so that if someone gets a recaptcha that they really can’t solve, they can click on the “reload” to get a new one.

   And, no, I have no idea what you are supposed to type for mathematics.

4. • CommentRowNumber4.
   • CommentAuthorUrs
   • CommentTimeMay 3rd 2011
   • (edited May 3rd 2011)
   • PermaLink
   Author: Urs
   Format: MarkdownItex> I have no idea what you are supposed to type for mathematics. Well, that's what I meant with my second message: over on [their webpage](http://www.google.com/recaptcha/learnmore) they explain that every now and then they will send a sequence of symbols of which the serving computer in fact does _not_ know what the correct corresponding key-sequence is and in these cases it is not actually the user whose non-robotness is being tested, but the user is secretly asked to do a favor to globalized automatic text recognition. So that explains why whenever the text is genuinely unreadable or even contains mathematical symbols, then every input from my side is accepted: the software does not test me, but learns from me in these cases. I like that idea. I like Google scanning and text-recognizing books, and I like the idea that solving Captchas, annoying as it is, means contributing a tiny little bit to that effort.

   I have no idea what you are supposed to type for mathematics.

   Well, that’s what I meant with my second message: over on their webpage they explain that every now and then they will send a sequence of symbols of which the serving computer in fact does not know what the correct corresponding key-sequence is and in these cases it is not actually the user whose non-robotness is being tested, but the user is secretly asked to do a favor to globalized automatic text recognition.

   So that explains why whenever the text is genuinely unreadable or even contains mathematical symbols, then every input from my side is accepted: the software does not test me, but learns from me in these cases.

   I like that idea. I like Google scanning and text-recognizing books, and I like the idea that solving Captchas, annoying as it is, means contributing a tiny little bit to that effort.

5. • CommentRowNumber5.
   • CommentAuthorAndrew Stacey
   • CommentTimeMay 3rd 2011
   • PermaLink
   Author: Andrew Stacey
   Format: MarkdownItexAh, I see. You hadn't realised that there was anything other going on than the non-robot verification. Yes, that's why I picked this particular Captcha-variant.

   Ah, I see. You hadn’t realised that there was anything other going on than the non-robot verification. Yes, that’s why I picked this particular Captcha-variant.

6. • CommentRowNumber6.
   • CommentAuthorUrs
   • CommentTimeMay 3rd 2011
   • (edited May 3rd 2011)
   • PermaLink
   Author: Urs
   Format: MarkdownItexAh, okay. No, it wasn't clear to me at all. They should say this more prominently: > Please fill out the following. Apart from this being a small annoyance to you, your effort will in fact contribute to the great plan of wikifying all of mankind's knowledge.

   Ah, okay. No, it wasn’t clear to me at all. They should say this more prominently:

   Please fill out the following. Apart from this being a small annoyance to you, your effort will in fact contribute to the great plan of wikifying all of mankind’s knowledge.