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This is in reference to closed question:

Is the following predicate logic formula is valid

While I can understand the reason for closing it, I do have to disagree with closing it. In my view it sends the wrong message.

When I first saw the question it immediately reminded me of the quantifier section I just read in How to Prove It: A Structured Approach . Specifically example 2.1.4 which list all of the combinations of for all and there exist with the variables x and y and condition x < y for natural numbers. Velleman then goes on to explain the validity and meaning of each one. (Sorry I can't list them here because Meta doesn't display LaTeX)

So while the question given may be very basic, I personally found not only the question and answer to be of value, but also the link to Mathematics for Computer Science.

While the question was answered in a comment, someone else with more knowledge could have added more value with an answer. While I do recognize the question as part of a pattern to watch out for with quantifiers, I am still learning the patterns fuller ramifications.

For people taking this in a course with an instructor getting the feedback is trivial, but for me being a self-learner, seeing the question closed and referring to have such questions asked in a forum is disconcerting. For some it is hard enough when self-learning to feel confident enough to ask a question here or in public, but then to have it closed for that reason, it could just smash someone, especially a young person.

I also would dislike seeing these questions done in a chat. One of the points of SE is to ask a question and get an answer without having to read through lots other meaningless messages. Putting such questions into chat would do just that; require someone to wade through lots of fluff. On top of that, every time someone wanted to see if such a question existed they would have to additionally query the forum log.

If such questions need a new tag to identify them as such, then please create one.

I don't intend anything here to be taken personally, and hopefully haven't conveyed that.

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  • $\begingroup$ Thanks for raising the discussion; it is important we talk about these things. Nota bene: everybody with at least 500 reputation can cast reopen votes. Five such votes will reopen the question. $\endgroup$ – Raphael Aug 5 '12 at 11:42
  • $\begingroup$ "closed for that reason" -- which (perceived?) reason are you referring to? "it could just smash someone" -- I hope that the comments on the question explain sufficiently that the reason for closing was because of how the platform works, not because it is a "bad" question. " Putting such questions into chat would do just that; require someone to wade through lots of fluff." -- That assumes that anybody but the OP will be interested in the question as is, which I consider unlikely; individual feedback is required there (hence the closing). $\endgroup$ – Raphael Aug 5 '12 at 11:55
  • $\begingroup$ If anything, I conclude from this the need for a community that helps each other even if the request does not fit SE, which is a good thing! I would ask everyone interested to visit Computer Science Chat regularly so we can discuss questions unsuited for the platform there (or discuss whether a given question is suited). $\endgroup$ – Raphael Aug 5 '12 at 11:56
  • $\begingroup$ @Raphael The close reason I was refering to was "an extraordinarily narrow situation". Oh, I see your reason for using chat. I thought you wanted the question to be asked there and answered there without the posibility of being later introduced as a question on the main site. My mistake for misunderstanding. $\endgroup$ – Guy Coder Aug 5 '12 at 13:21
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I hesitated closing the question; it is a good question in the sense that it should be asked by a learner and discussed. I closed it because it is a poor Stack Exchange question. It should be asked in a situation where the asker can outline their ideas and proofs and the expert can give feedback along the way (the "whiteboard discussion").

It is true that the answer to the question implies how bad the question is here: the "yes" answer is minimally productive for the site, but a "no" answer would have needed to be more elaborate, and thus potentially useful.

As it is, the question asks to confirm (binary¹) solutions to specific exercises. It may be possible to edit it into a useful question (for example, ask for general properties of predicates $P$ so that the given formula is (not) fulfilled, or ask for a proof of one of the examples if there is only a gut feeling but no rigor in the OPs attempts). It is legitimate to do so after closing, and then vote and/or flag for reopening.


  1. Levi does not even give his proof attemps!
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I have no doubt that you are committed to answering questions to help others, it is the SE ethos that gets in the way. The SE ethos caused me problems when first coming here and parts of it still does to this day.

So do I understand correctly that you see the proper way for a person trying to confirm their answer when being a self-learner should be a "whiteboard discussion" and that as a discussion it does not belong on the site?

What I would like to see in the answers of such questions is what the question is trying to help the student understand from the material just presented and what it means in a bigger sense.

In each case, you have a countermodel if and only if the predicate causes the conditional to evaluate as false.

If that were put into an answer then I would have up-voted it since it helped me and others could see that by the up-vote.

Also thanks for reminding me I can vote to open.

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  • $\begingroup$ The problem is that a potential answerer can not know that kind of information would help the asker, if anything (he did come to a solution, after all). We do not know was he has understood and what not. Writing just something as an answer is not a fruitful approach. Therefore, the question needs to be written such that it is clear what an answer should contain. $\endgroup$ – Raphael Aug 5 '12 at 14:48
  • $\begingroup$ Confirming solutions is, especially in TCS, often possible by simple calculations/checks. Of course it is necessary to hone those verification skills at some point. Similar to programming, tests should be written/learned before content, so people in this situation should learn (maybe with the help of cs.SE) how to check their solutions. If there is no problem, answerers have little to go by. $\endgroup$ – Raphael Aug 5 '12 at 14:50

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