@WillieWong I've noticed your edit here. So I guess we should use pde instead of parabolic-pde and elliptic-pde. Since you answered quite a lot questions tagged pde, I think we should follow your opinion.

@Willie, is it really, truly worthwhile to have separate tags for each PDE class?

I've made the same retag here.

So (parabolic-pde) should be removed by SE software in the next 24 hours.

@JM In my opinion? No. See my answer math.stackexchange.com/questions/21525/…

@WillieWong Cool answer. :) So, we remove with prejudice then...

The split between parabolic, elliptic, and hyperbolic is a vestigial classification derived from the days of Hadamard when the world view is quite a lot simpler. (For starters, only 2nd order PDEs are considered interesting.) While it serves a purpose of describing some qualitative behaviours (for example that of regularity gain in the first two, maximum-type principles for the first two, energy methods for the last), there are lots of equations that do not fall in this classification scheme

@MartinSleziak I don't think it's a worthwhile tag to have.

The only argument I have in favour of retaining those tags is the advanced state of development of the theory of 2nd order ellipitc and parabolic equations compared to rest of the field. (With the exception of first order scalar equations where we have complete understanding). But in cases where the ellipticity or parabolicity really plays a role, I believe those are keywords that would be mentioned in the post (and hence searchable!) anyway, and the additional tags do not add value.

@JM I think Martin got that, seeing chat.stackexchange.com/transcript/message/5361231#5361231

@WillieWong Yeah, I see that that's the thing I untagged... :)

@MartinSleziak Also, I must say, that tag wiki was next to useless :-p For that same reason I never felt like writing a tag wiki for, say, [proof-strategy]...

@WillieWong "I believe those are keywords that would be mentioned in the post (and hence searchable!) anyway, and the additional tags do not add value." - that was what I was thinking when I de-tagged that question.

@WillieWong I am not exactly sure what is the purpose of that tag. So it's difficult to write tag wiki, if the usage of the tag is not clear.

@WillieWong That bit was my response to variables

So perhaps someone could post about variables in the long thread....?

@JM oh man, I even moved my mouse up to see the antecedant before I wrote my response. I must have aimed poorly...

BTW there was a question on meta about (proof-strategy) tag, but no answer.

The suggestion to remove (proof-strategy) in long thread has 2 upvotes, no downvotes.

Perhaps (notation) would be suitable for the question about variables for operations?

The one about free and bound variables could be (logic).

@MartinSleziak It's not so much a notation question, I think. More of "what operation does this?"

@MartinSleziak My impression of proof-strategy is that it is asking about "birds-eye" view of how to approach a problem. Sort of asking for heuristics on how one may approach a certain class of problems. A typical answer could be something like : "If you need to demonstrate such and such then you should use forcing." But I don't think this is the commonly accepted POV.

(But, certainly not algebra-precalculus)

@WillieWong sounds like the start of a tag wiki... now if only we can all agree on how to use the blasted tag properly.

@WillieWong That seems reasonable. Perhaps one might say that it is questions/answers similar to tricki articles. But I don't think it's the way it is used on MSE.

@MartinSleziak Ah, the tricki! That neatly captures what I had in mind. Well, since J.M. just bumped the meta, maybe we'll get some discussion.

ok

In any case, I should get back to work. Some computations are turning out unexpected stuff.

@WillieWong See ya. And thanks.

About variables: Should i post in the long thread (to see other opinions on keep/remove), or are we going to retag the 3 questions?

@MartinSleziak Yeah, post in the long thread. I got nothing on those three too.

ok

thanks to both of you!