I was contrasting "dialogue" with "monologue" (and soliloquy). Of course, dialogues can have more than two participants. The point being that they have at least two. Before posting an answer, I'd like to be sure that at least one person is going to read what I write. The only person I can be reasonably sure of is the person who asked the question (which is why I also want to know far more background than is usually given in questions to know whether or not what I write is close to what the person wanted). So if that person is no longer interested in the answer, then I'd like to know that. I will agree that deletion is possibly quite a strong way of sending this message, but I can also see that someone wouldn't like to have their name attached to a question that later turned out to be a bit silly.

If, in the meantime, other people have joined the dialogue then there is a case to be made for keeping the question alive. But if the original asker is no longer interested, it seems more logical for one of the new participants to repost the question - essentially claiming it for them - than to force the original asker to ask a question against their will. (I suspect that under the stated license, MO has the right to force the original asker to ask their question against their will, but that's a side issue.) That's why I said that Kevin, perhaps, should have asked-and-answered his own question if he felt that his work should not be lost to posterity. Please note, though, that what he had actually posted was a comment with suggestions on where to look. It was only later that Kevin did the substantial work and then couldn't find anywhere to write it. So he hadn't actually lost a significant posting.

To specifics:

@Mariano:

But he had already done something.

But he had not done anything significant. He had posted a comment. Comments are, by their very nature, not as important as answers. I certainly wouldn't consider anything in a comment reason enough to keep a bad answer/question. Putting something in a comment signifies that you don't view it as all that important since comments are often skimmed and only a small number are viewable.

Your description makes it sound a lot like a math twitter, really!

What's twitter?

I know for sure that my little part was most certainly not oriented towards that.

I could pick apart the whole of that section, but let me concentrate on this sentence. Why do you take part in MO? You are one of the higher rep people so I'm curious. I take part to help people, or to try to. Every now and then I try to get people to help me, but without overmuch success. But, as I've been trying to say, in order to help, I need to know that the other person still needs help and wants the kind of help that I can give.

@hanche:

erases the blackboard in the midst of discussion and leaves

For a start, someone sneakily keeps taking pictures of the blackboard so that it can be restored if needed. Secondly, 'fraid that's a snag with using blackboards! They get erased. If you want your work to be more permanent, put it on a wiki somewhere and make sure it's linked from all surrounding topics.

As we've seen, deletion is not permanent. And in this particular case, the blackboard wasn't filled with lots of calculations from lots of different people.

@David: I think you missed my point about primary purpose versus by-product. If you want to store up a database of useful bits of mathematical knowledge, MO certainly isn't the best way to do it. That this happens is inevitable, but to say that a question should be preserved because of some vague future benefit seems illogical. Who knows, maybe tomorrow there'll be a new Lurie paper explaining why the Bruhat decomposition is all a simply consequence of (infinty,38)-categories. If something is obviously worth preserving, then it's worth preserving somewhere better than the MO database.

MO is primarily about dialogue, not monologue and not soliloquy (monologues can have audiences). If one party to the dialogue decides - for whatever reason - that this isn't a conversation that they want to participate in at this time, then the dialogue ceases. – Andrew Stacey

Uh, but what about multilogue, for lack of a better word? If it's all about dialogue, why not use email? Think of a discussion around the blackboard in the commons room attracting three or four participants. Then the one who started the discussion decides he's tired of it, erases the blackboard in the midst of discussion and leaves. I for one would not be pleased if it were my calculations he just wiped out.

Of course, I sympathise with Kevin that he did some extra work and was frustrated that it went to waste. Unfortunately, that's the deal with MO. But there are other options available. He could ask-and-answer his own question. He could write a blog post about it. He could make a page on some convenient wiki about it.

He could do all that and many other things. But he had already done something.

I, for one, will probably not consider considering a question asked by someone with a tendency to delete other people's work...

Rather, MO's focus should be on the immediate: I want an answer to this question at this time. That's its strength, it should play to it.

If that's the focus it should have, then I guess I'll grow bored very, very fast with the site. Your description makes it sound a lot like a math twitter, really!

I really doubt the motivation behind what I consider the best parts of MO are anywhere near the focus nicely captured by the "I want an answer to this question at this time" mantra, bold and all, especially on the answering side. I know for sure that my little part was most certainly not oriented towards that.

My reason for this is that, as I've said before, MO is primarily a place for people to obtain answers to questions. If someone is no longer interested in obtaining an answer, then there is really little to be gained from answering it. This ties in neatly with the recent SBS post that tried to resurrect some ancient questions. One of those is vaguely interesting to me, but there are lots of questions that are "vaguely interesting" to me, and I only have a limited amount of time so before I think about it, I'd like to know who's really interested in having an answer. The only person who's interest I can really judge is the person who originally asked the question - people voting for a question doesn't give much indication as to how interested they are; do they mean that they, too, came across this question in their research? Or just that it sounds like a nice question to know the answer to?

An example that I recently heard makes this point very well. It was motivating a course in the technology of water systems. There were lots of pictures of consequences of pipe bursts: cars disappearing in Oslo and the like, but it was only when the person said that 50% of all water pipes in Trondheim (where I live!) are below standard that I realised that Yes, this was a very interesting subject!

To emphasise my point, I don't think that we should think of MO as building up a stock of answers for future generations of mathematicians to search through. The extent to which this happens is a happy by-product (I'd be interested to know how much this does actually happen). Rather, MO's focus should be on the immediate: I want an answer to this question at this time. That's its strength, it should play to it.

Of course, I sympathise with Kevin that he did some extra work and was frustrated that it went to waste. Unfortunately, that's the deal with MO. But there are other options available. He could ask-and-answer his own question. He could write a blog post about it. He could make a page on some convenient wiki about it.

MO is primarily about dialogue, not monologue and not soliloquy (monologues can have audiences). If one party to the dialogue decides - for whatever reason - that this isn't a conversation that they want to participate in at this time, then the dialogue ceases. There are better places for monologues and soliloquies.

Edit: I take issue with Kevin Buzzard's comment mainly for the last line. It makes me look like a jerk and a hypocrite, but that's not a fair characterization. First of all, I've already proven this. I was asking for a better proof. That's more "due diligence" than any question I've voted down for being in a standard reference can claim. Additionally, how can you honestly expect someone who's never seen the term "reductive group" before to be familiar with the references? I searched for something like proof of Bruhat Decomposition of GL_n on Google, Google books, and Wikipedia and was not able to find a reference. Granted, the last time I searched for it was right after the exam (probably a little less than a year ago), but that still doesn't mean that I failed to fulfill the necessary prerequisites for asking a question on MO.

I feel like people have a knee-jerk response whenever they see me on MO, and I don't think many people here are willing to give me the benefit of the doubt. However, I think I hold myself to the same standards I hold other people to, and I find it in bad taste for someone to challenge my integrity like that. I'd rather delete questions that have accusations like that than have to deal with them like this, because it's embarrassing that I have to keep doing things like this. I don't want to stand out as a whiner, but there are certain accusations that I have to respond to.

9

Open any book on representation theory of reductive groups? shrug Not an answer, but definitely what I would do. Did you try this? Is it in Borel/Humphreys/Jantzen/Platonov-Rapinchuk/Springer? The answer to your other question is "yes" though: a Borel subgroup is a maximal connected solvable subgroup, or a minimal parabolic, and P is parabolic if G/P is projective. A Weyl group is N(T)/T where T is a maximal torus and you could definitely find that in Borel/Springer/Humphreys... . Don't you usually vote down questions that can be trivially answered using standard references? ;-) – Kevin Buzzard 21 hours ago

You're hitting me with all of these words. I asked a linear algebra question. How does this have to do with anything you said? It's not really fair to assume someone is familiar enough with reductive groups to know the standard references on them. – fpqc 8 hours ago

@fpqc: your first, second, and fourth sentences are fair, but your third isn't. Kevin's comment describes a generalization of the situation for GL(V) to a much more general class of groups and what he is saying is extremely relevant to the question you're asking (especially the last one). – Qiaochu Yuan 3 hours ago 4

@fpqc: in particular, I think Kevin's response is perfectly reasonable in light of your explicit request for "more machinery." – Qiaochu Yuan 2 hours ago

What do people think? (Please, those involved, don't act unilaterally -- it would be best all at once or not at all.)

So much drama connected to a question is among the best demotivators ever.

In general, I agree that you shouldn't delete stuff unless there's a very good reason to do so. In particular, I think we should leave up answers that turn out to be wrong if they have any interesting content. But in this case, I think the deletion might have been justified. If you post a question and one of the first responses is the comment "Did you check [obvious resource you should have thought to check]?" and you haven't, then I think it's okay to delete the question. Once you look at that resource, you should come back and improve the question by incorporating whatever you learned. If you learned nothing, at least say that you checked. If you completely answered the question, I guess you should just leave it deleted.

The point is that if you happen to post a half-baked question, it's best to delete it quickly until it's fully baked. If you post a half-baked question and it gets answers, then I think you should leave it up and just do your best to make it reasonable. Really, you should try very hard not to post half-baked questions, but sometimes they happen.

It sounds cheesy, but we learn more from failure than success! Remember that questions and answers on MO are not just for you, but for future generations of mathematicians. Some of the best learning is done from the sort of Socratic exchange you had with Pete---and it's good learning even for we observers.