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Some nLab pages had a gray link to descriptive set theory, which now has the following stub:
Descriptive set theory is the study of the structures and hierarchies of subsets of real numbers (or more generally of subsets of Polish spaces) that are definable by formulas with real parameters in second-order arithmetic.
Such subsets include Borel sets and more generally projective sets that are defined by alternating between taking images under projection maps of previously defined sets and taking complements of previously defined sets. Once the domain of topologists of the Polish schools and Russian analysts of the early 20th century, it is now considered a central area of logic in which set theory and computability theory (recursion theory) meet and interact.
Ugh, I just noticed that “projective set” redirects to projective object, which is pretty bad. At some point today I’ll remove that redirect and write a stub for projective set, possibly with a note of disambiguation.
Okay, I’ve just recreated a stub for projective set with disambiguation. (Suggestions for usage guidelines or how to better say it are of course welcome.)
Urs, you are too fast!!
I was just going to create the stub. Apparently we created the page simultaneously, and the sotware has no means to deal with this. Anyway, your version is in effect, all is good.
Urs’s version (v3) seems to be the one in effect.
Do most people understand q.v.?
Urs’s version (v3) seems to be the one in effect.
Not on my system.(?)
(But there is something really strange going on. Check out the history, right now it gives me three entries rev#1 by Todd, rev#2 by me, rev #3 (current) by Todd. But just a few minutes ago it was different, there was then still a rev #4 by me, where I had reverted to Todd’s rev #1.)
I should have put a smiley on #4, and added that maybe I’m too slow. :-)
The current version I see is what I believe I had originally written for version 1 (but for the singular in the title, which I want, but which I had corrected to just before Urs’s version had appeared on my screen).
David, did I use q.v. incorrectly? I understand it (quod vide) to mean “(for) which see”. I think Toby knows this abbreviation, but if it’s too distracting it can be eliminated.
Re #7, are we talking about descriptive set theory or projective set? As for the latter, I added a redirect to the plural.
Re #8, it’s not that it’s incorrect, I was just imagining how many of my undergrads would know what it meant, and would bet on it being fewer than 1 in 20. If anything more than the evidential link is required, I guess a ’see there’ would be easier.
Makes sense. Putting such little trappings of scholarship on display is self-indulgent I admit (although I’m shocked, shocked I tell you, that British youth no longer know their Greek and Latin!).
I’ll remove it so that I don’t give more reason for people to want to give me a smack. :-)
1.4% of our youth study Latin to the age of 16. The vast majority will never have studied it. I doubt Greek even registers.
The only exposure is to the spell names in Harry Potter.
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