TeX, LaTeX and Friends

A: Community Promotion Ads - 2013

@JasonBourne It's been corrected; now the area of 254.34 :)

tohecz

1

leo

2:42 AM

hello

how do I put the functions arsec arcsc y arccotan in LaTeX

2:56 AM

@leo Do you mean how to typeset them or how to use them?

@Canageek Congratulations on getting into grad school. That's a long move.

leo

3:34 AM

@Alan Munn how to typeset them. Should I define them?

@leo If you load the amsopn package, you can declare a new operator with \DeclareMathOperator{\arcsec}{arcsec} etc.

@egreg @PauloCereda:

Valquíria Wagner

1 1

3:57 AM

@Speravir Likely a Brazilian.

@AlanMunn Because of the “í”?

@Speravir Yes. And there are plenty of German names in Brazil, so this is probably not that uncommon.

@AlanMunn This with the German names I know, but should there seriously be parents who give their child the name “Valquíria”? OK crazy things happen: chantalismus (you need to understand German).

@Speravir I don't think it's considered an outrageous name in Portuguese. And compared to some of the names Americans name their kids, your German examples are normal. :)

@AlanMunn If this is the real name, then the parents are great Richard Wagner fans.

4:23 AM

@Speravir Maybe. Do a google image search for "Valquíria Brasil" and you get plenty of regular looking people.

doncherry

5:28 AM

@HarishKumar You might be interested in copypastecharacter.com (another follow-up to tex.stackexchange.com/questions/93862/…)

leo

6:11 AM

By default, theorem counters restart when chapter counter step, right?

How do I set explicitly that behavior?

user19161

7:32 AM

@enderland Sometimes it is hard to find duplicates.

8:30 AM

@leo when you declare the theorem there is an optional argument eg [chapter] resets when chapter incremented, or in general you can use \@addtoreset to make one counter be reset when another is stepped.

9:09 AM

Here's what my profile page is saying today. :)

4

9:24 AM

@egreg ooh! :)

@AlanMunn, @Speravir: Valquíria is indeed a common name in Brazil (one colleague of mine has this very name). :)

Well, not that common, but it is OK. :)

10:02 AM

@egreg: I updated the patch, thanks for the suggestion. :)

morning folks :D

just had a great talk with some of jehovas witnesses its gonna be a great day :D

Andrew Swann

10:47 AM

@egreg A pity you missed the first 8 months of Tex.SX

Martin Scharrer

11:05 AM

@egreg Nice.

It's me second anniversary today. Just got reminded by getting my second Yearling badge.

user19161

@MartinScharrer At first, I thought it was your wedding anniversary, LOL.

Martin Scharrer

@JasonBourne :-) Well I'm not married to TeX.SX. At least not yet! ;-)

@MartinScharrer I now pronounce you man and \wife. :)

Martin Scharrer

@PauloCereda Ha Ha

@PauloCereda At least you made me the man in the relationship! :-)

@MartinScharrer :)

Sep 12 '12 at 20:08, by Paulo Cereda

A woman is much like TeX: forget something that matters, even a tiny little thing, and you are screwed.

2

11:17 AM

Woman inspires us to great things, and prevents us from achieving them.

user19161

@Timebandit Man does that too.

;)

I searched the meta site and the faq for something like a wikipage listing all capable online compilers /tool. does this page exist? If not do you think is would be a "nice to have"

Torbjørn T.

12:51 PM

94

Q: Compiling documents online

I have heard rumors that you can compile documents online, and more specifically that Google has a free online compiler, but I have never been able to find any. Is there a way to compile documents online, so that I can write and compile documents even if I don't have a TeX distribution installed ...

compiling tools online

@Timebandit Something like that one? (see Stefan Kottwitz' answer)

@TorbjørnT. ah exactly what i was looking for! there is a new page called www.Spandex.io. pretty nice with version control, parallel working and dropbox integration. can i add this one the the list in the answer?

Torbjørn T.

@Timebandit Sure.

1:08 PM

ooh power I can edit questions on SO now:-)

1:23 PM

@DavidCarlisle My rep on SO is 131. :)

@egreg I see we are head to head again (on the nobreak question)

@egreg pathetic:-)

@DavidCarlisle My answer to such questions starts automatically. ;-)

@DavidCarlisle I have three nobreaks here. :) Oh wait, we are talking about TeX.

@DavidCarlisle I'll downvote four answers of yours so you'll go below 2000.

@egreg 3 all so far, perhaps we should get Psmith to report current scores in such matches instead of Indian league cricket scores

1:29 PM

@DavidCarlisle ooh I like the idea. :)

1:49 PM

JeanValjean, Italy

113 4

algorithmicx arrays lists tables

o.O

Great, now wait a few moments for us to spot Javert in the userbase. :)

Nov 26 '12 at 16:58, by David Carlisle

@PauloCereda that's muttley:-)

@DavidCarlisle :P

@PauloCereda He promised me a glass of wine, recently. :)

@egreg Muttley? (It will probably have a stick of dynamite in it)

@DavidCarlisle No, JeanValjean. Oh, wait, not the one of "Les misérables".

2:00 PM

@egreg :)

@ℝaphink Hi!

Hi @egreg

Talking about French, here comes @ℝaphink! :) Hi! :)

Heh

user19161

@ℝaphink Your r makes you unpingable.

2:03 PM

Compose key + | + R

:-)

@egreg seems to know how to ping me :-)

user19161

That's too complicated for a banana like me.

@ℝaphink Click on the gravatar, copy the username, paste. :)

/me thinks about whether he would like to be pinged by bananas

@egreg, that works, too :-)

Look down, look down
Don't look 'em in the eye
Look down, look down,
You're here until you die

@PauloCereda: You're in a joyful mood it seems :-)

2:05 PM

@ℝaphink No "compose" key on the Mac

@ℝaphink Since we mentioned Les Misérables, the work song came to my mind. :)

On MacOSX at least

user19161

2:23 PM

I just witnessed a spectacular quarrel in another room. Three lines were removed. =)))

@JasonBourne Mortal Kombat! :)

user19161

@PauloCereda Two were removed by the author himself, one by a flag. The flag was a stupid one.

@JasonBourne ooh! :)

We could try triggering another fight here!

Lets see: bikinis².

Oh. :)

user19161

@PauloCereda It said "I have enough shit from her" without specifying who "her" is. What's there to flag? Even if "her" is specified, so what?

@JasonBourne Maybe it was implied in a previous conversation?

user19161

2:26 PM

@PauloCereda Yes, it is implied, but so what? Is the world supposed to take every line here seriously? If I say you are an asshole, is everyone supposed to believe me?

@JasonBourne Oh. :(

/cries

<3

@JasonBourne They don't have to believe you but it would be explicitly against the house rules (and likely to be flagged in other contexts) chat.stackexchange.com/faq#nice

2:43 PM

@ℝaphink Hey there. I've been playing around with eBooks recently. Any tips on how to make them look nice?

@AndrewStacey: what do you use to produce them?

@ℝaphink LaTeX using my own class (output is technically PDF which I then convert to text).

PDF to text will never look nice

@ℝaphink The resulting text is raw XHTML.

since ebooks are essentially HTML-based (at least mobi, epub, etc.), it's easier to convert directly from LaTeX to HTML

so you don't lose the metadata (titles, chapters, notes, etc.)

this is why I use TeX4HT for this job

2:46 PM

@ℝaphink loopspace.mathforge.org/discussion/15/… See the ePub link.

I get a clean XHTML (which I can tune with a .4ht file)

it doesn't look bad at all ;-)

@ℝaphink That's what my class does: converts from LaTeX to XHTML. It's just that as TeX only knows how to produce DVI/PDF, I need to then extract the text.

how so?

@ℝaphink "how so?" to which bit?

how so, you need to extract the text because TeX only knows about DVI/PDF?

TeX4HT can produce XHTML directly from TeX

2:51 PM

@ℝaphink Yes, I know that. But I don't know how to make TeX4HT work with other outputs which is where I started on this goal: use TeX to convert (La)TeX to XYZ. Anyway, the question was: what makes a good eBook?!

ah, good question :-)

I guess you'll get different answers from different people

I'd say the ease to access different parts (I struggled with indexes for example)

(or footnotes, which I chose to put after paragraphs)

typography as well (how well nbsps are kept for example)

what would you say?

user19161

I just realised there are two guys wearing sunglasses now.

user19161

One on the eyes and one on the hat!

I wear mine above my hat

that doesn't really count

@JasonBourne Mine are prescription so that doesn't really count either.

user19161

2:57 PM

@AndrewStacey Ah, you must be one of those who can't see too much light!

@ℝaphink Looking at what I produced, I'd say line breaking still needs a bit of work. There are various places where I'd like to say "Don't break there". Mostly between maths and punctuation (maybe @DavidCarlisle knows how to do that in XHTML).

@ℝaphink But I also want to explore what makes an eBook an attractive prospect. I'd like to be able to show another mathematician a mathematical eBook and have them say, "That looks really good. I'd like to do that with one of my papers/lecture notes."

right

hehe

you have seen mine, right (not math though)?

they're not perfect by any means, but there's probably good and bad things to say about them which might help to define what is a good ebook ;-)

@ℝaphink Yes, I've a copy of it on my computer. I like the look and style of it very much. I need to look into the code to see how you achieve that.

I've got several books

they're all listed here: cc-translators.github.com

@ℝaphink Ah, right. I have the "charismatique" one.

3:01 PM

ok

that's probably the nicest looking

one thing that has frustrated me a lot is that i've been wanting to use an horizontal separator

a decoration horizontal rule

but I want it to scale with the text

and I haven't been able to find a way that works with all devices

it seems images are always scaled to the page in epub

@ℝaphink True that they're not perfect. Which is one of the hurdles for getting them adopted. So if I can find good examples to show that even though they aren't perfect, they still have something positive about them, that'll help.

@ℝaphink What is SVG support like?

no idea

in general, I find the state of ebooks frustrating

PDFs look like real books, but they're not reflowable

@ℝaphink I'm up against it there with use of MathML. Very few ebook readers support it as yet.

and Epubs are reflowable, but they're a mess to produce and perform differently on different devices

it's like doing HTML in the 90s and trying to support 3 different browsers

@ℝaphink And ultimately, that's the point. Reflowable means (to some extent) accessible. So eBooks are accessible mathematics by the back door. Get people interested in producing mathematical ebooks and all of a sudden, they're producing accessible mathematics without realising it.

3:04 PM

how so accessible?

you mean for blind people for example, or for normal people? ;-)

(as in, with no math background)

@ℝaphink Blind, visually impaired, dyslexic ... all who need their material presented in a "non standard" way.

right

3:37 PM

@AndrewStacey I believe it shouldn't break before punctuation anyway if there is no white space but what implementations do is another matter. I assume you are using the apple ipad ebook thing (about the only one claiming epub3 mathml support currently:(

@DavidCarlisle It also breaks in Firefox 18.

hang on....

@DavidCarlisle Calibre's mathml support seems to be reasonable as well.

@AndrewStacey oh havent looked at that for a while (is that webkit based?)

@DavidCarlisle Don't know. Back to FF, there are plenty of bad linebreaks within MathML on math.ntnu.no/~stacey/documents/diffloop.xhtml but you'd have to adjust the width to get a break at the end of a maths tag.

@DavidCarlisle According to the user manual, calibre uses MathJaX for viewing: manual.calibre-ebook.com/typesetting_math.html

3:56 PM

@AndrewStacey Oh OK good but slow then:-)

@AndrewStacey so I can stop it breaking before the comma but the effect isn't quite what you might want ^^^^^

@DavidCarlisle True, but then I'm using Calibre on my computer so if I want decent maths rendering I'll use FF - Calibre's to convert it to epub.

<!DOCTYPE html>
<html>
<head>
<title>line breaks</title>
<style>
body
{
max-width:40em;
}
.nb {
white-space:nowrap;
}
</style>
</head>
<body>
<p>
one two three
one two three
one two three
one two three
one two three
one two three
one two three
one two three
one two three
one two three
</p>
<p>one two three
<math>
<mn>111</mn><mo>+</mo>
<mn>1</mn><mo>+</mo>
<mn>1</mn><mo>+</mo>
<mn>1</mn><mo>+</mo>
<mn>1</mn><mo>+</mo>
<mn>1</mn><mo>+</mo>
<mn>1</mn><mo>+</mo>
<mn>1</mn><mo>+</mo>
<mn>1</mn><mo>+</mo>

@DavidCarlisle On the other hand, given that the linebreaking within the maths is also dodgy, preventing linebreaking within maths and for any punctuation thereafter might not be a bad thing.

@DavidCarlisle So the span has to include the punctuation.

@AndrewStacey Yes there is an Open Bug on implementing the MathML3 linebreaking in firefox, they hoped to get some google code funding and a willing slave^H^H^H^Hstudent I think

@AndrewStacey yes apparently but also if you use another class on the nested math to turn the css property back to normal then it breaks before the comma again. I think the break is actually inside the math (at the very end) so hard to get any css to that point

@DavidCarlisle Mind you, if it is inside the maths then there could be a case for that being a rule in the implementation of MathML line breaking.

@DavidCarlisle Putting whitespace: nowrap; on the maths itself at least prevents the bad linebreaking within (even if it doesn't fix the punctuation). That already improves the look considerably. (My mathematics is short enough that the line break before or after doesn't look bad.)

4:27 PM

Hello

@GregRos 'ello.

Would you have any idea how to mirror or flip a tikzpicture? (it is a pgfplot; I need to mirror the plot itself graphically)

Oh. I guess I could just accomplish this using a parametric plot. Hmm. Let me see

If you have an idea how I would do so graphically though I'd still like to know :P

4:45 PM

@GregRos \reflectbox ?

AHA

Thank you. Scalebox and rotatebox did exactly what I wanted.

@GregRos what kind implementer added those to latex I wonder...

What do you mean?

@GregRos you'll figure it out:-)

michal.h21

5:12 PM

@AndrewStacey speaking of ebooks, github.com/michal-h21/tex4ebook now produces valid epub2 using just tex4ht, some lua scripts, tidy and zip

5

5:35 PM

Hmm. Is there a way where I can define an equation in an environment, and without having to use \let or \def or something, insert it into the text?

E.g. something like \insertref{name}

@GregRos what's the problem with \def?

Well, the idea is that if I'm working on some part of the text that is distant from where I defined the equation, and I hadn't \def'd it, I'd have to either go back, \def it, and replace it with the \def'd version, or copy it. Since I do not \def all my equations and theorems for obvious reasons, but I do \label most of them, it would be better if I could use a reference rather than a definition.,

That is kind of what references are for. To be referenced.

5:50 PM

@GregRos since tex is more or less procedural a macro or box ought to be defined before use. the ref label system works different. It writes to a auxiliary file. And ref uses this file to "find" the label. So i could think of a certain system which will write the definitions to a aux file and read them in in a second run. This would mean that the calls could be used even before the definition is seen by tex.

But there isn't something like it at present

@GregRos not around the common packages i suppose. But you might find something on ctan.org

I tried. I didn't find something promising

Well as i said it could be done, though i can't see a broader benefit. Commands should always be defined in preamble or at the beginning of the document. This is just a question of programming style

A: How to recall a figure without rewriting it

@GregRos I posted an answer on site just recently that let you make a copy (rather than just reference the number) of a figure, do you mean you want the same for an equation?

17

Updated to avoid duplicating the caption and label information. \documentclass{article} \usepackage{graphics} \makeatletter \def\savefloat#1{% \expandafter\def\expandafter\@endfloatbox\expandafter{% \@endfloatbox \global\setbox#1\copy\@currbox}} % Stephan Lehmke's \leaders trick to stop...

6:01 PM

@DavidCarlisle i believe he wants a call before the definition (or filling of the box)

A: What's the difference between JavaScript and Java?

6:20 PM

This question can be closed as too localized: tex.stackexchange.com/q/94153/2693 (problem solved by installing MacTeX).

575

Java and Javascript are similar like Car and Carpet are similar.

As a linguist, I find this wonderful.

6:40 PM

@AlanMunn +1

Silex

7:09 PM

@AlanMunn Indeed!

How does 'changing' a question work? (Inspired by this question).

@DavidCarlisle:

This is madness!!!!!!!!!!!!

Comando não encontrado => Command not found.

7:52 PM

@PauloCereda any properly configured machine will act that way

@DavidCarlisle There was no emacs either. :P

@PauloCereda so it is just a toy, not a real computer at all

@DavidCarlisle :P

10:8 to @egreg in the nobreak question. There is no justice in the world

8:06 PM

What is it about today, this morning a question about redefining \number and this evening redefining \fi ....

4

@DavidCarlisle Simple solution: get on with xor. LaTeX3 has none of these problems :-)

@JosephWright as soon as latex is mainstream people will figure out where we hid the primitives and change catcodes and redefine random xparse internals...

8:21 PM

@DavidCarlisle Then we have people who don't read the manual: tex.stackexchange.com/questions/94278/using-siunitx-in-captions/…

@JosephWright how can you type so fast? tex.stackexchange.com/questions/94278/using-siunitx-in-captions

@bloodworks 1) I can touch-type, more-or-less 2) I know the answer to this without having to think about it :-)

@JosephWright ✌

(unicode definitely has too many useless chars)

@bloodworks Also ones that are so small they don't look like anything!

@JosephWright looks better when bigger. I suppose we cannot controll the font size in the chat?

8:30 PM

@bloodworks 𝚞𝘯𝗶𝕔𝒐𝕕𝕖 𝕕𝙚𝘧𝒾𝖓𝙞𝗍𝘦𝗹𝑦 𝚑𝖆𝓈 𝖙𝒐𝘰 𝘮𝘢𝘯𝗒 𝓾𝑠𝚎𝒍𝔢𝗌𝘴 𝖈𝗁𝒶𝖗𝒔

5

@bloodworks Well I could see it when I zoomed up a lot

I see the WriteLaTeX ad has made the main page

@DavidCarlisle ✔

8:50 PM

@DavidCarlisle Our readers know better. :P

@DavidCarlisle Redefining \fi causes one of the best error messages in LaTeX: the TeX runs stops with Missing \begin{document} and the error line shows exactly \begin{document}. :)

@JosephWright Did you see the user's nickname?

9:06 PM

@egreg Yes: and?

@JosephWright Er, what does it mean in Spanish?

Somebody has been flagged for talking about bikinis.

@egreg No idea

@egreg Yes, I saw that

@JosephWright es.wiktionary.org/wiki/cojón

@egreg Doesn't really help :-)

@egreg The user has had an account on SO for 3 months

@egreg I'd read it as 'elco-Jon'

@JosephWright Click on the English page; here it is, anyway: en.wiktionary.org/wiki/cojón

@JosephWright Low traffic user. I'd raise an objection.

9:14 PM

@egreg OK

@egreg Not quite sure how to handle this: I will have to seek advice!

Any thoughts on tex.stackexchange.com/questions/94282/siunitx-with-svg-graphics? I've tried to reproduce without success.

9:32 PM

@egreg I found meta.stackoverflow.com/questions/37942/policy-on-display-names on user names, but so far nothing on ones that are non-English. Still looking

@egreg Also, I can't really judge how bad it might be viewed

@JosephWright Would you accept the nickname "Thebo**ocks"? I think you can easily fill in the blanks. ;)

@egreg That's partly my point: the way it's described in WikiPedia sounds more like 'TheB**ls'

@egreg Also, if you start on non-English names it could get very complicated: there are lots of 'traps' here (there are after all lots of languages)

@egreg It's also been pointed out in the TL that the username in question does not include the accent, so it's not the same word

@JosephWright Unfortunately there's no Spanish speaker here. The missing accent is just a "cover up".

My biggest problem is I can't find an official position one way or the other to refer to

@egreg Possibly

@egreg The user does not appear to be Spanish, by the way

@JosephWright Ask the Powers That Be. If they say it's OK, good.

9:40 PM

@egreg Well I've asked in the TL: I'll try again

@egreg Perhaps a Meta.SO question is in order

@egreg I've got some feedback from the Powers, and have politely asked the user to change the name

@JosephWright Thanks.

@egreg Apparently I can force through a name change, but I'll hold off on that (not quite sure how to do it, for a start!)

Ah, worked it out :-)

I think I'll give the user a little while first before doing that

user19161

There is a guy on math called Harry Potter's Erect Nipples.

@JasonBourne That's up to the mods there to worry about

@JasonBourne There are lots of strange people in Math.se. :)

9:51 PM

@JasonBourne Also, probably not offensive, just wierd

user19161

Weirdness and offensive are all relative of course. =)

user19161

@JosephWright weird

@JasonBourne Oops

user19161

@egreg Maybe the people here are stranger but choose not to display it. =)

@JasonBourne Well, I just read an answer telling to use cofactors for inverting a matrix.

10:35 PM

@PeterGrill I've seen your answer and it wasn't going to work. First, the new \RN should be \protected because it starts with a conditional; second, as you redefined it, \oldRN would always find \fi as its argument (biblatex's \RN has an argument) and so \expandafter\oldRN\fi is needed to get rid of \fi

11:03 PM

@egreg Well good thing I noticed that you answer was similar.

@PeterGrill That \expandafter\macro\fi is sometimes handy. :)

11:17 PM

booktabs mafia: almost as bad as the tikz crowd

@PeterGrill Perhaps better:

\documentclass{article}
\usepackage{booktabs}
\usepackage{amsmath}

\begin{document}
\begin{tabular}{ c c }
\toprule
\textbf{EKF} & \textbf{UKF}\\
\midrule\\
\addlinespace[-2ex]
$Q = \begin{bmatrix}  0.1 & 0 \\ 0 &  0.1 \end{bmatrix}$ &
$Q = \begin{bmatrix} 0.01 & 0 \\ 0 & 0.01 \end{bmatrix}$\\
\addlinespace[1.5ex]
$R = 5 \times 10^{-3}$ & $R = 5 \times 10^{-5}$ \\
\bottomrule
\end{tabular}
\end{document}

@egreg Ok, yes that is a lot less hackish than my solutions. And what is @DavidCarlisle doing actually answering the question that was asked?? :-)

@PeterGrill I don't know; sometimes he tries.

@egreg :-)

What is the correct macro for a conditional/biconditional? I have been using \to/\leftrightarrow but wondering if there is something I should be using...

@PeterGrill Somebody uses \Rightarrow and \Leftrightarrow.

11:27 PM

@DavidCarlisle: You really have to stop answering what is asked, but instead answer what they should have asked. But, since you have helped me so often I;ll give you a n easy tick: The solution to http://tex.stackexchange.com/questions/94307/why-does-defining-a-newcommand-inside-a-framed-block-not-work is \global\def\myText{Bliblibli!}. :-)

@PeterGrill No the better solution is to move the definition out of the environment

@egreg Who is this somebody? I don't think a double arrow is approriate for implication.

@DavidCarlisle Yeah, but sometime it needs to be inside -- something that won't come across in a MWE.

@PeterGrill I beg to differ. Defining a command inside an environment should be discouraged if it's not just for internal usage. And so it must be local, generally speaking.

@PeterGrill You won't find that kind of arrows in many higher level mathematical logic books.

@egreg Agreed... BUT, there are cases where it needs to be otherwise. But that was almost a year ago when I need tex.stackexchange.com/questions/51733/…, so perhaps I would do thing s differently now... But that solution is working great for me...

isn't a double arrow the norm for that hence `\iff`\iff:
macro:->\;\Longleftrightarrow

11:31 PM

@DavidCarlisle I thought \implies, \iff was when it was known to be true, where as in a logic statement the conditional/biconditional can be false.. Or am I mistaken here?

@PeterGrill hmp egreg got more than me there as well:(

@PeterGrill That's a very special application.

@DavidCarlisle You should learn how to use \patchcmd. ;-)

@PeterGrill using iff when you know the lhs is true is a bit pointless (as the "only if" part refers to cases when it isn't true)

@DavidCarlisle Well egreg was faster... I think I have both your solutions coded with a switch that I can go between one or the other if I even encounter a problem, but don't recall ever having to switch since I first used it.

@egreg I never like loading a package that uses more code than I need.

11:34 PM

@PeterGrill I don't follow you. The truth value of a conditional statement depends on the truth values of the components.

@PeterGrill "If 5 is even, then 15 is divisible by 6" is a true statement.

@DavidCarlisle Huh? $p \to q$ has one case where it is false, but a \implies b does not? Or at least that is my understanding of the difference between the sigle line arrow and the double line arrow.

user19161

Is this math or programming?

@JasonBourne math.

Hey, you are not the real Jason Bourne are you? :-)

user19161

@PeterGrill My name is just a label. I am who I am, a sentient being in the Wheel of Samsara. =)

@JasonBourne All names are labels. We really should be assigned IP addresses when we are born so that we all have a unique identifier, just like everybody else. :-)

user19161

11:40 PM

The only way for "a implies b" to be false is when there is a case when a is true and b is false.

user19161

Otherwise, the conditional statement is true mathematically.

user19161

So "if 1=2, then 3=10" is true because 1 is not 2!

user19161

"a iff b" is equivalent to ("a implies b" and "b implies a").

@PeterGrill You're mixing language and metalanguage.

user19161

Outside mathematics, what we say above doesn't apply.

11:47 PM

@egreg In an intro to logic course, when first encountering implication, would you use $p \to q$ or $p \Rightarrow q$?

user19161

By the way, the amount of cursing and swearing these days is Math > Eng > TeX chat rooms. =)

@JasonBourne Wow, sounds like the Math chat room is more fun :-)

user19161

@PeterGrill I try to tell people not to curse so much because there are many flaggers. We don't want unwanted attention...

@PeterGrill Most often the single arrow is used for "formal language" (where we don't look at the "meaning" of the symbols), the double arrow for implications in the metalanguage.

user19161

Also, the double arrow is usually reserved as a shorthand. In ordinary mathematical prose, words are used instead.

11:49 PM

@JasonBourne Sounds tensors are too tense for some people :-)

user19161

So open a mathematics book and one doesn't see double arrows, but words like "if a, then b".

user19161

However, in lower level texts, these double arrows are not uncommon.

user19161

Lots of overlap between theoretical computer science, mathematical logic and philosophical logic.

user19161

Many people hold appointments in more than one of these three departments.