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I asked a question on the main site. One of the users suggested to edit it and delete some parts which are covered by a Wikipedia article. When I did it, one of the answerers complained that by the new version half of his answer is not useful and is irrelevant somehow.

I'm not sure what should I do now and if a part of my question is in a Wikipedia article, does it mean I cannot ask it? I saw another question which was about definition of some DB expressions and no one complained why you asked an easy question and I didn't think it was easy.

I asked four questions and had the same problem about two of them, is there any special levels for the questions or contributors that I'm not aware of?

Also I saw some unnecessary edits being done on my questions.

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    $\begingroup$ When you start a meta discussion about a question, please link to the meta discussion in a comment on the question. $\endgroup$ – Gilles 'SO- stop being evil' Mar 12 '12 at 2:21
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When you ask a question here, we'd like to see that you have put in some effort towards solving the question yourself. If the second section of the Wikipedia article on the topic you ask about is the answer to your question, that indicates you may not have put in much effort in answering your own question before posting it here.

You can find some more information on this here.

When you ask a question, also say what you've already found out on the topic and why you ask that particular question: that way, we can help you better, and you may give users more incentive to answer your questions.

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  • $\begingroup$ I know, I'm not new to SE and CS seems to work exactly like MSE. But I wanted to add a part and I could just write "I have no idea what to do about this", which is not very nice to say. $\endgroup$ – Gigili Mar 10 '12 at 20:08
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    $\begingroup$ @Alex I don't fully agree with what you say. For this specific situation, the wikipedia page lists the operations which are closed, but this is a partial answer. Here we have a chance to give some insight as to why these operations are closed and others are not, and maybe give some proofs. Even if the question was a Yes/No question, we should assume that the one asking it wants to know why the answer is Yes or No. It is also better for the people to search this question later. $\endgroup$ – Ran G. Mar 10 '12 at 20:16
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    $\begingroup$ Then the question should be improved to ask that question ('I've seen the list of closure properties on Wikipedia, but I'd like to know how their proofs go'), which is to some degree what @Raphael was doing. As the question seemed to be about what happens if you intersect infinitely many CFLs, I can understand why he decided to cut out that one sentence as it contained a quite different question. Note that the main purpose of my answer is to describe why I think the edit was made, and not because I think the edit was the best thing to do. $\endgroup$ – Alex ten Brink Mar 10 '12 at 20:28
  • $\begingroup$ Please note that I did not change the content of the question. See my answer. $\endgroup$ – Raphael Mar 11 '12 at 22:29
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My edit has been criticised for changing the question too much. Please note that you can look at a question's (or post's) revision history by clicking on the edit time. As you can see in this case, the OP changed the content of the question, I merely adapted it to use proper notation and notions.

For instance, I replaced $+$ on sets with the proper $\cup$ and changed the title; the phrase "an infinite sequence of languages is context-free" just does not make any sense.

This (imho) improving edit was since rolled back by the OP which suggests to me that they do not even recognize proper notation resp. that the question was still equivalent, which in turn means the OP did not research the topic at all before asking.

In general, questions that ask for facts that can easily be found (e.g. on Wikipedia) are not useful on our site. Questions that ask for explanation of something that can easily be found can be great; after all, Wikipedia articles often lack precision and rigor.

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  • $\begingroup$ You're in no position to judge if any research has been done or not, I wanted to ask what other people think. I'll flag your answer as offensive because of these parts: "just does not make any sense", "the OP which suggests to me that they do not even recognize proper notation resp", "the OP did not research the topic at all before asking". $\endgroup$ – Gigili Mar 11 '12 at 13:29
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    $\begingroup$ @Gigili I have not judged, I have formed an opinion. Like it or not, this is the impression you made on me. If this offends you, maybe you should take more care to clarify what you have done? Again, you use notation and wording that is non-standard or outright wrong (as in mathematically meaningless; for instance, a sequence of languages can not be member of a language class, the types just don't add up) and reject efforts to help you express your question better. Tell me, how should I interpret your behaviour? $\endgroup$ – Raphael Mar 11 '12 at 13:46
  • $\begingroup$ @Gigili Trying to build a case by quoting me out of context does not help your position, either. $\endgroup$ – Raphael Mar 11 '12 at 13:46
  • $\begingroup$ Non-standard in your opinion, it's one of the questions in my final exam and I wanted it to be exactly like that. so we're learning non-standard notations here, thank you for letting me know! $\endgroup$ – Gigili Mar 11 '12 at 13:54
  • $\begingroup$ I don't think discussing notation is the main point here. $\endgroup$ – Raphael Mar 11 '12 at 14:35
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(Involvement notice: I edited one of your posts.)

There are many different points in your meta question, I'll try to address them all.

I don't think any of the edits on your posts were unnecessary. Keep in mind that on Stack Exchange, other users can edit your posts, and this is very much by design. Once you've posted a question, it belongs to you and to the community. In a private beta, most involved users read every post, and you can count on a lot of scrutiny. The people who edit your questions are trying to help by improving the way your questions are formulated, formatted or classified; this will help you get better answers.

In the question you linked, if I follow correctly, there were two edits, one done by you at the request of Raphael and one done by Raphael himself.

  • I can't see anything objectionable in Raphael's edit. He improved the title and the formatting of mathematical notations. I don't understand why you rolled it back.
  • The second part of your question, “Does the properties of regular languages (closed under intersection, concatenation, etc.) apply on context free languages as well?”, is rather broad, and it is covered to a large extent by the Wikipedia articles about regular languages and context-free languages. There are several sub-issues here:

    • Stack Exchange does not aim to reproduce Wikipedia or other reference sites. There has been some debate in introducing a general reference close reason. This has only been done on a few sites, mostly because there is a lot of potential for this close reason to be abused. Even if there is no directly associated close reason, you should read the “obvious” Wikipedia article(s) before asking a question. If there's something you don't understand in the article, say that you've read it and tell us what part you didn't undestand.
    • Each Stack Exchange question is one question. If you have several questions, ask them separately.
    • The second part of your question was rather broad, and I can see that people may have considered too broad for a Stack Exchange answer.
    • That being said, I would have interpreted that second part as a follow-up to the first part, and not as a complete question on its own. That is, rather than delete it, I think it would have been better to restrict it to the operation you considered in your main question, i.e. the union.
    • In general, you should not make substantial edits to a question after posting it, especially if it invalidates existing answers. However, if the question is not suitable in its present form, this takes precedence: if you've asked two questions in one and different people have answered different parts, then
      • this shows why you should not ask two questions in one;
      • you should do your best to make your question suitable, and if you can't do it without invalidating an existing answer, try to cause the least harm.
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  • $\begingroup$ Good answer. Let me add one point. When looking into something new you usually do not know the established notions, especially if rediscovered a concept on your own. In this case, a question is bound to read badly researched. In this case, experts should give a good reference before voting down or closing. The OP can then adapt (or retract) the question in a timely manner. $\endgroup$ – Raphael Mar 12 '12 at 8:19
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    $\begingroup$ @Raphael If the asker evidently wasn't aware of a standard notion, then the question should not be closed or downvoted, but answered with the name of that notion, a short explanation and a pointer to learn more. $\endgroup$ – Gilles 'SO- stop being evil' Mar 12 '12 at 8:22
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There is no problem with asking questions for which an answer appears in Wikipedia.

Maybe the issue is that your question contain two questions. Why not separating it into two questions and then moving the appropriate answer to the appropriate question?

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  • $\begingroup$ As a Comment I would say you can re-edit your post to contain both questions, by simply asking what are the closure rules for CFLs for various operations, and does it matter if the operations are carried out finite or infinite times. $\endgroup$ – Ran G. Mar 10 '12 at 19:57
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    $\begingroup$ No, Stack Exchange does not aim to reproduce content that's already available in some reference document. See Introduce a "general reference" close reason and other discussions on this subject. There's no consensus as to where to draw the line, but reproducing Wikipedia is clearly out. “I've read the Wikipedia article and didn't understand <this>” is a good question; asking “what is X” when the WP article for X is a fine answer is not. $\endgroup$ – Gilles 'SO- stop being evil' Mar 12 '12 at 2:20

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