# Talk:Main Page

Welcome to the general discussion page of $\mathsf{Pr} \infty \mathsf{fWiki}$. Please add any new discussion topics at the bottom of this page. |

Archive 1 |

## Well-orderings: sets and classes

I'm looking again at the properties of well-orderings and order isomorphisms in the context of class theory, still using Smullyan and Fitting as my mentor.

During the course of this I am finding they derive some results which take certain truths of bijections and order isomorphisms for granted, but they themselves do not prove these results (e.g. Composite of Order Isomorphisms is Order Isomorphism and Inverse of Order Isomorphism is Order Isomorphism and so on) are fairly trivial and which we have proved in the context of **sets** not **classes**.

It is at this stage where I am tempted to expand the scope of these latter results and rework them in the context of class theory not just set theory.

I am not sure at this stage whether to make them class-theoretical results only, and just add "they apply to sets too" or implement a separate class-theory version only ("This result carries over to classes as well:" etc.).

Bear with me while this is all a bit of a mess still. --prime mover (talk) 05:28, 6 July 2022 (UTC)

- The inexhaustible prime mover... --
`Ascii`

23:00, 6 July 2022 (UTC)

- I confess I am getting a little tired, staring at it and not making any sense of it. --prime mover (talk) 23:12, 6 July 2022 (UTC)

## Another stage implementing class theoretical approach

Fundamental results in well-order theory in the implementation of the class-theoretical approach require that all the basic algebra of set composition (composition, identity and inverses basically) in the context of ordered sets need to have their class-theoretical versions.

Work is to take place in due course, after I've had a break from it for a short while. --prime mover (talk) 21:33, 9 July 2022 (UTC)

### Shortcut City

In order to drastically simplify the entire area, I am currently experimenting with leaving a lot of the basic definitions alone, but merely removing the stipulation that the domains and ranges of the mappings and relations in question are in fact sets.

Hence we start with "Let $f: S \to T$ be a mapping" and leaving it up to the context for the reader to determine for themself what the nature of the domain and range actually are. To those raised on set theory only, they will understand that $S$ and $T$ are sets because it is implicit in the definition. To those raised on class theory, the class-theoretical definition is found under the "class-theoretical definition" subpage of the definition page for mapping and relation.

I have a further idea to streamline the whole area: use the term **collection** consistently when referring to a collection which may be either-a-class-or-a-set-and-the-definition-is-identical-for-either, and somewhere on the page on which this appears, transclude a boilerplate page explaining $\mathsf{Pr} \infty \mathsf{fWiki}$'s philosophy on the matter: "On $\mathsf{Pr} \infty \mathsf{fWiki}$, the term **collection** is specifically and unilaterally defined as being ..." and so on, explaining why we do that. Then we never have to worry about splitting the pages up into "class-theoretical version" and "set-theoretical version" but merely rely upon the context from which the definition page is linked.

(And the weather is going to be glorious today and I have household chores to do before going to a piano concert this afternoon so I'm not planning on spending all day at the keyboard today, despite the fact that I have awoken bright and shiny -- so I don't plan on doing all or any of this today.) --prime mover (talk) 08:06, 10 July 2022 (UTC)

- I saw the curse of class theory on here years ago. It's so interesting that it might finally see its defeat.
`Ascii`

01:09, 17 July 2022 (UTC)

## Sanity check

Just checking the following theorem isn't on the site (can't find it): let $X$, $Y$, $Z$ be topological spaces. Give $X \times Y$ the product topology. Let $f : X \times Y \to Z$ be continuous. Then for $x \in X$, the map $y \mapsto \map f {x, y}$ is continuous as a map $Y \to Z$. We called this the $x$-vertical section in measure theory. Basically hinges on the continuity of $y \mapsto \tuple {x, y}$. Caliburn (talk) 10:17, 19 July 2022 (UTC)

## How to describe exactly the theorem I want to find

I am now trying to find the proof of this theorem: $a^s>1$ when $a>1$ and $s>0$, but so far I haven't found it. I am not a native English speaker, how can I accurately describe the theorem I am trying to find in natural language? --AuroraAeon (talk) 02:25, 23 August 2022 (UTC)

- It is possible that theorem does not exist on $\mathsf{Pr} \infty \mathsf{fWiki}$. This is because it wasn't included in the source work upon which the bulk of the basics of real analysis was built. --prime mover (talk) 05:34, 23 August 2022 (UTC)

- The best I found is this: Power Function on Base Greater than One is Strictly Increasing, which states $a^s > a^0 = 1$ when $a > 1$ and $s > 0$.
- For what it's worth I used the following on Google: "site:proofwiki.org power greater one". — Lord_Farin (talk) 06:05, 23 August 2022 (UTC)

## Notation Confusion

You see, there's a lot of pages in the site like this, which writes stuffs like "Let $a\in \mathbb{C}$ be a complex number.

Is it really necessary?--AuroraAeon (talk) 00:28, 25 August 2022 (UTC)

- 100%. No confusion about what $a$ is. Convenient reinforcement of housestyle, too. The page Definition:Complex Numbers notes alternative symbols exist in the literature:
- "Variants on $\C$ are often seen, for example $\mathbf C$, $\CC$ and $\mathfrak C$, or even just $C$."

- Constantly being explicit and saying $\C$ means "complex numbers" increases styling uniformity.
- Not necessary in a single book with a few authors. But, a smart investment for a $40,000+$ page wiki.
`Ascii`

01:28, 25 August 2022 (UTC)

- What he said.
- Let me add: we don't write "Let $a\in \mathbb{C}$ be a complex number." We write "Let $a \in \C$ be a complex number."
- Note the difference. It's not particularly subtle. --prime mover (talk) 06:00, 25 August 2022 (UTC)

- I got it. Where can I obtain a systemic knowledge of the common-used housestyle in $\mathsf{Pr} \infty \mathsf{fWiki}$?--AuroraAeon (talk) 06:39, 25 August 2022 (UTC)
- Found it here, but thank you anyway.
- By the way, I notice that the archive of this page hasn't been updated for a long time.--AuroraAeon (talk) 06:47, 25 August 2022 (UTC)

- Yes it's been a busy year, but as there are a number of discussions which may not have been resolved I'm not ready to archive it yet. --prime mover (talk) 09:03, 25 August 2022 (UTC)

## Mathematicians pages - include family?

I'm throwing this open to debate, since this came up:

Is there any value to adding a "family" section to the Mathematician pages? That is, a section that gives the mother and father and perhaps also children of the mathematician?

My immediate reaction to this is "no, it's too much work and too tangential" but then on some of the pages we *do* have mentions of family -- specifically when those family members are also featured in our database.

So is it worth setting up another formal section to the Mathematician pages titled "Family" (or "Lineage" or whatever)?

Before I settle the question with a big fat "no" I want to see what others think. --prime mover (talk) 09:01, 25 August 2022 (UTC)

- No thank you. I would not forbid mentions of family, but only put them there when they could be of interest, i.e. when the family member can stand on their own. Otherwise it's just fluff. /2c — Lord_Farin (talk) 11:49, 25 August 2022 (UTC)

## New simple proofs for Logarithm Tends to Infinity and Logarithm Tends to Negative Infinity

Hi

ln e^a = a

let a = ∞ , e^∞ = ∞ ln ∞ = ∞

let a = -∞ , e^-∞ = 0+ ln 0+ = -∞

Also these proofs not found on Wikipedia https://en.wikipedia.org/wiki/List_of_limits .

## Order Notation - resolving the various confusions

Having become mentally and psychologically blocked on class theory and ordinal theory, I've found myself addressing Definition:Order Notation.

In an attempt to find something definitive, I have dug out my cobwebbed old Thomas H. Cormen, Charles E. Leiserson and Ronald L. Rivest: *Introduction to Algorithms* with an eye towards the fact that they cover everything in some detail, and appear to be consistent in their approach.

However, their approach is **different** from that taken by the various definitions I've seen, and I'm about to take a view on whether they merit genuinely different and parallel definitions, or whether we can implement an "also defined as" approach.

The CLR approach defines, for example, $\map \OO {\map g n}$ as the **set of functions**: $\set {\map f n: \exists c, n_0 \in \N_{>0}: \forall n > n_0: 0 \le \map f n \le c \map g n}$.

(This of course presupposes the fact that $f$ and $g$ are positive, and $f$ and $g$ are sequences rather than real functions, etc. so there will need to be adjustment of this to match the reality of what is what in pure mathematical contexts.)

As a result I may need to make several run-ups to this topic and maybe backtrack a fair bit.

Please bear with me while I have the scaffolding up. And please, if you see something that you know is obviously wrong in this area, put it up in a talk page rather than editing the page in question, as in that way we avoid edit conflicts and wikiwars. --prime mover (talk) 07:38, 27 August 2022 (UTC)

## Proof Rules refactoring executed

Hi all, the refactoring which had been prepared at User:Lord_Farin/Sandbox/Proof Rules has been executed.

The net effect is that our proof rules and rules of inference have been made ready to accommodate more than propositional logic, in particular also predicate logic. And that it is now much easier to build a new proof system on top of these rules in a coherent manner. This opens up further and more thorough coverage of predicate logic and propositional logic. My focus will be on PredLog going forward.

This mainly means that there are new and rewritten pages Definition:Natural Deduction and Definition:Rule of Inference. The old pages have been saved in my backup realm User:Lord_Farin/Backup.

What follows is a number of source review activities related to this change. I have access to a number of them, but not all.

The whole list is on the preparation page User:Lord_Farin/Sandbox/Proof Rules at the bottom. Any help appreciated. — Lord_Farin (talk) 10:31, 2 September 2022 (UTC)

- I have a number of the works in question -- if you don't have them I probably do, so assign them to me. I can always reassign them if I can't do them for any reason. --prime mover (talk) 12:02, 2 September 2022 (UTC)

- I did the works I could locate and assigned the rest to you. — Lord_Farin (talk) 09:28, 4 September 2022 (UTC)

- Yes okay it's on my radar, but it's not a trivial exercise and I will need to get myself back into the mindflow of each of the books to do a proper job. Been distracted with irritating trivia. --prime mover (talk) 09:30, 4 September 2022 (UTC)

## Philosophical quibbling over "undefined"

Show of hands here: is it reasonable to accept the tacit implication that if $a = b = 0$ then $a$ and $b$ are not coprime?

If $a = b = 0$ then GCD of $a$ and $b$ is **not defined**.

Hence **by implication** $\gcd \set {a, b}$ is **not equal to $1$**.

Are there philosophical constructs in which a function "being undefined" can also have the same truth value as the function actually having a specific value at the undefined point?

I am afraid I have wasted enough time on this utterly pointless argument, and I'd like either a little backup or to be told explicitly that I don't know what I'm talking about. --prime mover (talk) 11:06, 4 September 2022 (UTC)

- The definition is fine, especially now that Coprime Integers cannot Both be Zero exists. A pinch of accuracy would be gained by saying "$\gcd\set{a,b}$ exists and is equal to $1$". This mostly serves as a safeguard against simplistic application (compare limit and integral identities) and is not strictly necessary. — Lord_Farin (talk) 11:51, 4 September 2022 (UTC)

- I hate the fact that this is even considered worth doing, but clearly we seem to need
*something*of the sort. --prime mover (talk) 12:09, 4 September 2022 (UTC)

- I hate the fact that this is even considered worth doing, but clearly we seem to need

- There are two positions possible. We could argue that if one part of an expression is undefined, then the entire expression is undefined.
- We could also argue that a statement like $m \perp n$ is shorthand for: $\exists \tuple{ m,n } \in \set {\tuple {a, b}: a \: \mathrm{coprime \: with} \: b}$, the truth set of the relation. Then $n \perp 0 \iff n \in \set{ 1 , -1 }$ is a true statement, as $\tuple{ 0,0 }$ does not lie in the truth set, and this would be my position. - I believe that was the original problematic phrasing. --Anghel (talk) 13:11, 4 September 2022 (UTC)

- I'm still not sure there never was a problem. I wonder what the consequences are if we just carry on as we were. --prime mover (talk) 21:55, 4 September 2022 (UTC)

## Extension to the template `{{TFAE}}`

Is there any chance that the template `{{TFAE}}`

can be extended to accept an axiom: page as an alternative to a definition: page? Otherwise a definition: redirect to the axiom: page is needed. --Leigh.Samphier (talk) 13:28, 15 September 2022 (UTC)

- Yes of course, good call. I can get on and do that in due course. --prime mover (talk) 13:55, 15 September 2022 (UTC)

## Disambiguation of Quotient Mapping

The concept of a Definition:Quotient Mapping is fairly well case-hardened into $\mathsf{Pr} \infty \mathsf{fWiki}$ as the mapping from a set to the set of images of the equivalence classes under a given equivalence.

In topology, we have a definition Definition:Quotient Mapping (Topology) which is (at least on the surface) different in concept from a Definition:Quotient Mapping.

To add to the confusion, we have a Definition:Quotient Topology which uses the Definition:Quotient Mapping in its definition.

It also seems as though Definition:Quotient Mapping (Topology) is closely tied to the Definition:Quotient Topology, a.k.a. / closely related to the Definition:Identification Topology which uses the Definition:Quotient Mapping in its definition.

Is it advisable at this stage to rename Definition:Quotient Mapping to e.g. Definition:Canonical Surjection (there's already a redirect) to allay confusion -- or is there a way of knitting Definition:Quotient Mapping (Topology) and Definition:Quotient Mapping so that the latter can be immediately seen as being a special case of the former?

Advice needed to a) reduce confusion and/or b) improve cohesion. --prime mover (talk) 07:55, 19 September 2022 (UTC)

- Don't know if this helps.

- If $f:\struct{S_1, \tau_1} \to \struct{S_2, \tau_2}$ is a Definition:Quotient Mapping (Topology), then there is one and only one homeomorphism $r: \struct{S_1/\RR, \tau_\RR} \to \struct{S_2, \tau_2}$ such that:

- $f = r \circ q_{\RR}$

- where:

- $(1) \quad \RR = \set{\tuple{x, y} : x, y \in S_1: \map f x = \map f y}$ is an Definition:Equivalence Relation

- $(2) \quad \tau_\RR$ is the Definition:Quotient Topology induced by $\RR$

- $(3) \quad q_\RR: S_1 \to S_1 / \RR$ is the Definition:Quotient Mapping

- --Leigh.Samphier (talk) 11:06, 19 September 2022 (UTC)

- I have just uploaded a proof for Leigh Samphier's theorem: Quotient Mapping Induces Homeomorphism between Quotient Space and Image (where I renamed $r$ as $\tilde f$). The homeomorphism $r: S_1 / \RR_f \to S_2$ will be defined so:

- $\map f s = \map {r}{\eqclass s { \RR_f} }$

- If we squint our eyes enough to remove $r$ from this equation, and ignore the fact that the image set of $f$ is $S_2$ rather than $S_1 / \RR_f$ (which makes sense, as $r$ is a homeomorphism ), we can pretend that $f$ is a quotient mapping in the standard definition. --Anghel (talk) 20:41, 19 September 2022 (UTC)

- To address the disambiguation question. The definition of Definition:Quotient Mapping (Topology) for a
**quotient map**is ubiquitous.

- The definition Definition:Quotient Mapping is variously called one of
**canonnical/natural****surjection/projection**and rarely called**quotient map**. I personally dislike the use of**natural**as it most often indicates an informal left to the reader notion. I dislike the use of**projection**for sets as this seems inappropriate, but is appropriate in algebra settings where the question being asked is whether an algebra is the direct product of a subalgrebra and the quotient of the algebra by the subalgebra ($A = S \times A/S$).

- That only leaves
**canonical surjection**, which I have reservations for its use as it isn't suggestive of the involvement of an Equivalence Relation. But nothing else comes up. --Leigh.Samphier (talk) 09:43, 20 September 2022 (UTC)

- After further thinking. For the record, I'm happier with
**canonical surjection**than**natural blah blah**-- but now I think about it, I really don't like abandoning the "quotient" term which underpins the understanding, and is common to the whole gamut of quotient structures.

- After further thinking. For the record, I'm happier with

- As the Definition:Quotient Mapping (Topology) is indeed a construct also (indirectly) created from an equivalence relation, and therefore
*is*the "same sort of thing" as a more general Definition:Quotient Mapping, I now think we should leave the names alone (they are consistent and logical) and if necessary add an explanatory note transcluded from a subpage to explain the situation.

- As the Definition:Quotient Mapping (Topology) is indeed a construct also (indirectly) created from an equivalence relation, and therefore

- You could add a theorem that showed that a Definition:Quotient Mapping where the set and quotient set are endowed with discrete topologies is indeed a Definition:Quotient Mapping (Topology). I can't decide if this is illuminating and completes the loop or is plain clumsy. --Leigh.Samphier (talk) 10:36, 20 September 2022 (UTC)

- I wonder whether we should perhaps be making more of the "explanatory note" style pages. I note that sometimes "Note" and "Remarks" sections (which I like to make $\mathsf{Pr} \infty \mathsf{fWiki}$ try to steer clear of) could / should be evolved into "/Explanatory Note" pages, as we have done -- which will help to make it more obvious what is central to the information on the page and what is peripheral, discursive and explanatory.

- Evolution is a continuous process. --prime mover (talk) 10:05, 20 September 2022 (UTC)

- There is definitely a place for explanatory notes, and they need to be formal in the sense that they are a sequence of statements where each statement begins by referencing an existing theorem/definition and restates the conclusion/defining conditions of the theorem/definition. There should be no statements that are not referencing an existing theorem/definition, stubs should be avoided. With a correctly structured sequence the explanation should follow. --Leigh.Samphier (talk) 10:36, 20 September 2022 (UTC)

- I have just put up a theorem Continuous Surjection Induces Continuous Bijection from Quotient Space, which uses both Definition:Quotient Mapping and Definition:Quotient Mapping (Topology) in its statement. I ended up using Definition:Canonical Surjection instead of Definition:Quotient Mapping to avoid confusing the readers, just for this solitary case. I would like to know if anybody has a better solution.

- For the record, I also like the name Definition:Quotient Mapping better than any of the suggested alternatives. --Anghel (talk) 22:42, 22 September 2022 (UTC)

- A sensible approach. --prime mover (talk) 05:51, 23 September 2022 (UTC)

## Closed Curve vs. Closed Contour

I have tidied up and rationalised some of the work concerning Definition:Contour, Definition:Closed Contour and their instantiations in the complex plane.

During this, I noted where "closed curve" had been used to mean "closed contour" when it was obvious the latter is meant.

However, in the general context of geometry, outside of the realm of analytic geometry and complex analysis that the definitions of Closed Contour are defined, the term "closed curve" is not so easily defined as "contour". While Definition:Curve is more-or-less straightforward, it is not at all obvious how "closed" should be written in terms of pure geometry without invoking the language of mappings.

Anyone care to have a go at Definition:Closed Curve? --prime mover (talk) 07:51, 6 October 2022 (UTC)

## Originality and Novelty

Can I publish proof that is written by i.e me, on Proofwiki. Lets say I discovered a way to solve ax^-1 + bx + c = 0 equation to find x (which i actually did), and it is undeniable, but doesn't have authentic sources, should I go on contributing it?

- I think, as long as it is not a variation of a trivial fact written in extremely nonstandard notation, original proofs are fine. For example, the example you gave is a variation of quadratic, so it does not really warrant its own separate page. This is not an academic journal so it should not be used as a shortcut to publish results. But if you have a useful nontrivial lemma, it should be fine. Of course, others will have to double check for possibility of errors.--Julius (talk) 19:32, 16 October 2022 (UTC)

- The problem generally with original work is that instead of writing proofs of interesting toy problems or offer unfamiliar approaches to known theorems, (both would be very much at home here) people tend to claim proofs to unsolved conjectures causing some amount of upset when the incorrectness is pointed out. In your case multiplying through the equation by $x$ gives a quadratic so I imagine it'd just replicate work already done elsewhere. That said if you have an interesting obscure way of proving the quadratic formula that'd fit here. Caliburn (talk) 19:43, 16 October 2022 (UTC)

- My answer is: although you may think you have invented something new, you probably haven't. I thought I'd discovered the Stern-Brocot process till someone got me a copy of Knuth etc.'s Concrete Mathematics. A little disappointing when you find someone's been there before. You may be lucky, but don't bank on it. --prime mover (talk) 20:45, 16 October 2022 (UTC)

- Thanks everyone ☺️, after a lot of thoughts I owe thanks to everyone and reach the end to say, the point of user Julius is valid here. The following is an unfair abuse of academic journals and this place is a wiki, it can't provide any information about authentic research. Thanks user Calibrun and sorry, its a altogether new formula i made that doesn't require equation to be multiplied by x. Last but ain't the least, thanks to Prime Mover :) I think perhaps I am lucky because I couldn't find any result of this derivation of my formula on Wolfram Alpha, Arxiv and Google Scholar searches. Thanks so much everyone and the topic I wanted to add is definitely not eligible and I respect it. --Aitzaz Imtiaz(talk) 20:28, 17 October 2022 (UTC)

- What you could also do is start typing your result on your personal page here and make it more general over time. Although we avoid extremely trivial results, simple but interesting results could find their place here. Just don't rush to put your name in the title. Anyway your contribution will be visible under "View History".--Julius (talk) 21:46, 17 October 2022 (UTC)

## How reliable is Sasane?

Several definitions sourced from 2017: Amol Sasane: *A Friendly Approach to Functional Analysis* have been called into question.

Is this source seriously unreliable? --prime mover (talk) 18:10, 25 October 2022 (UTC)

- So I think there are two different things. The actual mistake regarding convergence to $0$ was well spotted and fixed. I guess I forgot to add that detail. I also believe that after I finished with that chapter I invited everyone give their opinions, and, finally, this is happening. The second issue is the style of definition pages of sets, spaces, etc. What I used to write is
**Let x be y. Then set of all x is z**. In my mind, the construction with**let**was not to be understood as fixing**x**to one particular instance. In other words, in this context I treated**let...**as an analogue of the axiom schema. However, other people read**let x be y**as fixing**x**. Then the set of all**x**will contain only that single instance. If we agree that this is a problem, then I will have to go over other pages where I followed a similar approach.--Julius (talk) 23:14, 25 October 2022 (UTC)

- So I think there are two different things. The actual mistake regarding convergence to $0$ was well spotted and fixed. I guess I forgot to add that detail. I also believe that after I finished with that chapter I invited everyone give their opinions, and, finally, this is happening. The second issue is the style of definition pages of sets, spaces, etc. What I used to write is

## Directed Sets and Nets

There currently exists ambiguity and inconsistency when referring to Definition:Directed Set and Definition:Net (Preordered Set). Namely, whether it concerns a preordered set or an ordered set that has the "directed" property.

I've taken up the task to disambiguate and restructure this, and would welcome other perspectives.

Content discussion and suggestions can be posted here or on User:Lord_Farin/Sandbox/Nets. — Lord_Farin (talk) 11:05, 5 November 2022 (UTC)

- My strategy is to leave it up to you to add your own angle to this, then see what you did and comment as necessary. I know enough about this area to know that I don't know enough. --prime mover (talk) 19:13, 5 November 2022 (UTC)

## Spambot attacks

We are seeing a large inflood of spambots applying for $\mathsf{Pr} \infty \mathsf{fWiki}$ accounts. These accumulate over time until the queue gets filled with irritatingly large numbers of these to be blocked. I have taken to blocking their input addresses as I go. Don't know if this helps.

I've been doing this for a couple of weeks now, and I find there may be 10 or 30 a day, but I am about to take a few days away from civilisation, so I can't do anything about this until after the weekend.

If anyone with admin privs takes on the thankless and infuriating task of dismissing spambot applications and at the same time blocking their IP addresses while I am away, that would be wonderful.

Please be careful, there are often some genuine applications from actual real people in the mix, so careful not to dismiss those as well.

Thanks in advance. --prime mover (talk) 08:21, 11 November 2022 (UTC)

- It has indeed been an innoying influx of bots. I'll try to keep the backlog in check. — Lord_Farin (talk) 17:05, 11 November 2022 (UTC)

- Last night I disposed of 31 spambot account applications. This morning 8 hours or so later I disposed of another 16.

- How easy would it be to change our captcha technique so as to screen spambots out before they get to this stage? --prime mover (talk) 08:55, 20 November 2022 (UTC)

- Ugh. Got home from work just now, checked the list, and 92 spambot applications since this morning at about 7. So whatever you did seems not to have worked. Sorry. --prime mover (talk) 17:44, 21 November 2022 (UTC)

- Definitely seems to have done. Nothing has appeared overnight. --prime mover (talk) 07:02, 22 November 2022 (UTC)

UPDATE: Whatever you did seems to have been defeated, because it's bad again. 15 spam attacks overnight. --prime mover (talk) 06:25, 24 November 2022 (UTC)

- And it's got bad again. --prime mover (talk) 17:28, 30 November 2022 (UTC)

- Whatever. Bots will be bots because they don't, and will never, understand what it really is to be human. --prime mover (talk) 20:06, 6 January 2023 (UTC)

## Changes to Template:TFAE/TFAENocat

I've recently made some changes to the templates Template:TFAE and Template:TFAENocat to allow Axiom: pages to be included.

If you notice any issues with these templates let me know and I'll fix the issue or reverse the changes. --Leigh.Samphier (talk) 02:16, 20 November 2022 (UTC)

- Thanks Leigh, we'll run with them. Good job. --prime mover (talk) 06:05, 21 November 2022 (UTC)

## Maintenance and good practice

I've been taking a look at some of the large quantity of common redlinks: Special pages:

https://proofwiki.org/w/index.php?title=Special:WantedPages&limit=500&offset=0

... and wonder if anyone has any particular knowledge of these areas can construct a simple definition for any of these objects.

Appreciate you may not be able to source them, but if you leave a `{{NoSources}}`

template in place they will not be deleted out of hand -- however, there should be sources around for such basic concepts. I suggest using the same language that is used in the book in which the concepts are used. --prime mover (talk) 21:17, 2 January 2023 (UTC)

Please feel free to help out with some of the basic stuff I'm posting up out of dictionaries and encyclopedias and so on. I'm working on areas I haven't looked at in many years. I am feeling my age. --prime mover (talk) 21:17, 2 January 2023 (UTC)

- That is a helpful list, although it is scarily long - the reason they are redlinks is probably because no simple definition is available.

- Presumably those who have been active in the fields in which there are large numbers of redlinks are (a) working from source books, in which case there ought to be
*some*definition of the concepts used, in which case it should be straightforward (albeit irritating and tedious) to transcribe from there, or (b) one knows the material so well one does not need to -- in which case, if it is not possible to define the concepts, one may not know the material as well as one thinks. --prime mover (talk) 06:58, 4 January 2023 (UTC)

- Presumably those who have been active in the fields in which there are large numbers of redlinks are (a) working from source books, in which case there ought to be

- I have written the two things I know about: Definition:Radon Measure and Linear Span is Linear Subspace. --Anghel (talk) 16:08, 3 January 2023 (UTC)

- Brilliant start. Anyone else? --prime mover (talk) 16:20, 3 January 2023 (UTC)

- I have noticed several redlinks related to differential geometry. I have been leaving out certain things because they were not needed for my work, but the paperwork has been submitted, and in principle I could start filling in the missing pieces. I could also tackle basic definitions for physics.--Julius (talk) 11:59, 4 January 2023 (UTC)

## A general shout out about categories

While it is quick and easy to just bung every definition into the top level bucket, it is suboptimal.

Can I request that contributors, when carving out a new field, try to subcategorise their definitions to a finer degree than just shovelling everything into, for example Category:Topology or Category:Ergodic Theory and so on?

Examples abound of how this is done. --prime mover (talk) 07:52, 3 January 2023 (UTC)

## Vector Spaces and Norms thereon

I have noticed a bit of a hole in our coverage of vector spaces.

Many sources, particularly if they are biased towards applied maths and physics, and so all their working is in the context of a real/complex vector space, gloss over the fact that to define the length of a vector, the underlying division ring of the vector space has to be normed.

Hence, in order to discuss anything to do with vectors having lengths, or norms, or whatever, we have to presuppose that such a vector space is indeed normed.

However, in many places we refer to a general "vector space", whereas we need really to invoke "normed vector space".

A case in point is Definition:Dot Product. In a general $n$-dimensional vector space, this is defined as $\ds \sum_{i \mathop = 1}^n a_i b_i$ where $a_i$ and $b_i$ are the components of the vectors. But then we have definition 2 which is $\norm {\mathbf a} \, \norm {\mathbf b} \cos \angle \mathbf a, \mathbf b$, where $\cos \angle \mathbf a, \mathbf b$ is the angle between $\mathbf a$ and $\mathbf b$, which, if you follow the link, is actually defined only on $\R^n$. So the two definitions are only actually equivalent in the context of $\R^n$ (which of course is all we're interested in when we're discussing basic physics).

If anyone cares to dig into this in depth and analyse carefully where norms are invoked, please feel free to comment both here and in the various relevant associated talk pages. --prime mover (talk) 08:37, 12 January 2023 (UTC)

## Updating the Featured Proof

The featured proof on the Main Page has been not changed in a year. To celebrate our 25,000th proof, can we find a new proof from the candidate list at *Category:POTW Candidate* ? --Anghel (talk) 12:44, 26 January 2023 (UTC)

- Feel free to update it to something you like. I hadn't realised it had been up there so long. --prime mover (talk) 13:14, 26 January 2023 (UTC)

- I would nominate Pi is Irrational/Proof 1 as the next featured proof, as it is described as a classic. Any suggestions from other users? I will update the featured proof by Monday. --Anghel (talk) 18:01, 26 January 2023 (UTC)

- That works for me. --prime mover (talk) 18:05, 26 January 2023 (UTC)