Mathematics - 2012-04-09 (page 4 of 6)

David Wallace

12:00

Oh, sorry, I must have David confused with someone else then. Thanks, @Gigili for pointing out my error.

Gigili

No problem. I live to please.

David Wheeler

i WISH i was 36. look out ladies, here i come! but, alas....

i have, as the saying goes, traded my hard drive, for a floppy

David Wallace

7 hours ago, by David Wheeler

my age is no big secret...i am 50

David Wheeler

i said that 7 hours ago! i'm much older now.

Gigili

Uh-oh. 57?

David Wheeler

12:03

ah, gigili, if i was 80 years younger and still had both my legs....

Gigili

I'm younger than 7 hours ago.

David Wheeler

i was born almost exactly 20 years after ringo starr

Gigili

Okay, I give up.

David Wallace

I thought for a moment it must have been the "David K", who has a blue-checkerboard gravatar that looks very much like that of Mr Wheeler.

David Wheeler

that blue david thing is gonna catch on. i can feel it.

David Wallace

12:06

... and who is also from Texas.

... but who claims to be 28. Younger than both of us put together.

David Wheeler

hey, i'm not just "from" texas...i was BORN here. i even know some racists. true story.

Gigili

Who's David K?

t.b.

this guy

Gigili

I'll have nightmares about different kinds of David.

t.b.

Glad to know that I'm too stupid, but I knew that already.

David Wallace

12:17

@Gigili He's the one you were referring to when you said

Mar 23 at 1:16, by Gigili

I got confused which David was the old one

I only remember this because I briefly thought you meant me.

Kannappan Sampath

@tb ? No trace of you there except you cast a close vote--does that involve a 10k feature or some such?

t.b.

@KannappanSampath not at all. "You guys are just too stupid to see it". It's gone for good now.

Gigili

Doesn't sound familiar, must be amnesia.

David Wallace

Might have been some other Gigili.

but she certainly looks a lot like you.

Kannappan Sampath

@tb Oh, I see...I don't like so much of noise... I'd defend I am not. :) [Yes, I know that's arrogant but can't help when OP is not making much sense too.]

t.b.

12:23

@KannappanSampath it looked like spam when it was first posted and it didn't get better...

Kannappan Sampath

@tb Hmmm. I have not visited main for a long time.

Gigili

@DavidWallace I am the only Gigili in the entire world.

David Wallace

facebook.com/gigili.alquitela

I think not.

@Gigili Back at you!

David Wheeler

oh wow...that IS a watchband....

Gigili

@DavidWallace Hugh.

David Wallace

12:31

Yeah, I originally thought it was a big dangly earring, but if you look at the large version of the photo, it's definitely a watch.

David Wheeler

funny...one of middle names is hugh

David Wallace

... but speaking of having nightmares, I'm off to bed. Good night, everyone.

Gigili

Night.

I knew you will say that.

David Wheeler

and clairvoyant, too!

what am i thinking now...um, don't answer that...ok, now its safe. go ahead.

t.b.

oh, well, good luck, sandra :)

@Gigili you asked about rob. he's here.

Kannappan Sampath

12:40

I am sad about Indianisms in English... I have fallen into traps several times but not as bad as Recent Victor post on meta. I wonder why does that guy flatter himself doing stuff he has little or no idea about.

Gigili

speechless

Henning Makholm

This one?

David Wheeler

what's an indianism?

Kannappan Sampath

@HenningMakholm Yes.

@DavidWheeler Look at the title--That's the right way of saying what he intends to say in Hindi, an Indian Language...But, it does not work that way in English...

Henning Makholm

@DavidWheeler A language error caused by the speaker/writer copying patterns from an Indian language (Indian English or native subcontinental?) which do not exist in that form in English (or whatever the target language is).

Daniil

12:44

Hi

David Wheeler

ah, like a french guy saying it not makes cold.

Henning Makholm

Is it just me, or has Victor's English become less comprehensible over the past handful of months?

t.b.

Is there a measure for that?

I always found it impenetrable.

Kannappan Sampath

I only sincerely feel that I get corrected often by native speakers--I don't want to speak something in English that sounds horrible or hilarious to a native speaker. My accent is bad too, very few people here would already know.

Henning Makholm

@tb Some sampling of old questions of his indicates that it probably is just me.

David Wheeler

12:49

@KannappanSampath can i ask you a personal question?

Henning Makholm

@KannappanSampath Speaking of which, the meaning of the first part of that post is not clear to me. Do you mean that non-native speakers don't often correct you, or that you're insincere when you feel non-native speakers correct you?

Kannappan Sampath

@DavidWheeler Depends--Ask and if I think it is OK, I'd answer that...

@HenningMakholm OK. I should have said: I would like to corrected often by native speakers. :)

David Wheeler

where you live, is there a large value placed on being polite?

t.b.

@HenningMakholm He had a few questions that he copied more or less directly from somewhere. Those might have looked slightly better than the usual ones.

Kannappan Sampath

@DavidWheeler Mostly yes. Elderly people would expect that of you.

t.b.

12:52

The problem with his questions is that they reveal only part of the truth because the worst ones are deleted.

Daniil

@KannappanSampath Ah, I understand you. I wish I would get corrected by native speakers more often :p

David Wheeler

from what other people have told me, english is a difficult language to master, partly because the rules aren't very rigid.

Kannappan Sampath

@Daniil Reading that again, I see, that is horrible too. But yes you're right. But I missed a "get".

Henning Makholm

@DavidWheeler Is English worse in that respect than other natural languages?

Matt N.

Am I allowed to have a little bit of a whine?

t.b.

12:54

shoot

Kannappan Sampath

@DavidWheeler BTW, is this that personal question you referred to?

Matt N.

I think the topic I picked for my BSc's thesis is difficult.

t.b.

What did you pick?

Daniil

Nah, English is quite easy, @HenningMakholm. For example, in Russian we have different verb forms in past tense, depending on the gender of the object.

David Wheeler

I don't know @HenningMakholm it seems "looser" to me than other languages i've learned a bit of, but my experience is limited

Matt N.

12:55

Algebraic topology.

Henning Makholm

@MattN That's good. Otherwise completing it wouldn't impress anybody.

4

Daniil

also, grammatical cases.

Kannappan Sampath

@HenningMakholm I had exactly that to say. +1

David Wheeler

@MattN i did my thesis on algebraic topology, too, for my BA, unfortunately, i've forgotten most of it.

Matt N.

@HenningMakholm I've been thinking about changing it to something "easier" but I've made a similar mistake once before in choosing something I'm not interested because it allowed me to go abroad.

Gigili

12:57

@Daniil Very true. It's fairly easy as opposed to German.

Matt N.

I know almost nothing about algebraic topology.

Henning Makholm

@DavidWheeler Isn't the "A" in "BA" for "arts"? Where does algebraic topology fit there?

@MattN Just ask Asaf. He's quite the expert.

3

David Wheeler

i was a math major at a liberal arts college

Matt N.

: D : D

I'll ask him about diagram chasing.

Kannappan Sampath

LOLzzzz...

@MattN Beware, he might chase you ... instead of the diagram :p

t.b.

12:59

@DavidWheeler I believe it is rather easy to get to a certain level that enables you to communicate, because you need and hear it all the time. On the other hand, you hear and read bad English all the time -- to the point where it is difficult to tell if you get accustomed to bad habits of non-native speakers or whether it's actual English.

Matt N.

: )

David Wheeler

and i have poor habits...i used to pride myself on my command of my native tongue, but life has corrupted me most foully.

Matt N.

I thought I'm unlikely to get a chance to see any of it later and also I wanted to do something that's not easy.

Ok. Now I feel slightly better.

takes tissues, wipes away tears and blows nose

David Wheeler

you'll be fine, Matt

you're smarter than i am, and i muddled through it, so so can you

Daniil

I've been watching too much American TV and films which heavily influenced my English skills. So now I use stupid "idioms" like 'man', 'dude', 'could care less', etc.

Matt N.

13:03

@MattN (^slight exaggeration)

Kannappan Sampath

@MattN We get that. :)

David Wheeler

@Daniil it's all part of our evil plan for world domination by exporting culture that lowers world intelligence

Matt N.

@KannappanSampath That almost sounds like an in Soviet Russia joke : )

David Wheeler

in soviet russia that gets YOU

Kannappan Sampath

@MattN I don't know what is that joke you're referring to! Culture differences, I think.

David Wheeler

13:06

Yakov Smirnoff

Yakov Naumovich Pokhis (, ; born 24 January 1951), better known as Yakov Smirnoff, is a Ukrainian-born American comedian, painter and teacher. He was popular in the 1980s for comedy performances in which he used irony and word play to contrast life under the Communist regime in his native Soviet Union with life in the United States, delivered in heavily accented English. He owns a theatre in Branson, Missouri, where he performs year-round. Smirnoff is also a professor at Missouri State University and Drury University where he teaches "The Business of Laughter." Early life Smirnoff was b...

Daniil

@MattN it's assume that complicated challenges improve your personal growth rates. I do not know anything about your area of study/work, but you give an impression of a really smart person, so I think you'll be fine

Matt N.

@KannappanSampath In Soviet Russia, diagram chases you!

And on internet, meme chases you! : )

David Wheeler

the classic "in soviet russia" joke is: "In America, you go find party. In Soviet Russia, party find YOU."

Kannappan Sampath

Oh, Thank you @MattN

Matt N.

@DavidWheeler That's in the video I linked. : ) The commercial is where the meme came from.

@Daniil Thank you! I wonder how I managed that : ) (I'm a maths undergrad)

David Wheeler

13:08

the reference being to being hounded by the communist party for any small social infraction

Kannappan Sampath

@DavidWheeler Thanks for this.

t.b.

Reminds me of the old Googling joke where you could feel lucky when looking for Chuck Norris and land here

Matt N.

The link gets hidden by mouse-over menu. Well, "history" will do.

David Wheeler

ah, chuck norris

Gigili

Matt N.

13:11

@tb : D

Daniil

@MattN yeah, but I thought you were a grad student, because you touch upon topics, which looks quite complicated from my point of view

Matt N.

@Daniil It looks quite complicated to me too. Teddy bear will confirm that I don't really know what I'm doing (yet) : )

Benjamin Lim

hey guys

Matt N.

Even though it's not actually complicated. When I learn something new it looks so "advanced" and a year later I realise just how basic it is : /

Benjamin Lim

who has a copy of scott osbourne's basic homological algebra?

David Wheeler

13:16

teddy bear???

t.b.

@MattN he won't. Teddy bears don't believe that there are topics that are easier than others. It's what you make of them.

Benjamin Lim

hey teddy do you have a pdf copy of that book?

t.b.

No, I don't.

David Wheeler

and i can make a hat, or a plane, or a sailboat....

Benjamin Lim

ok

thanks for it

I tried this whole afternoon

Matt N.

13:17

Did it work? I didn't test it.

It was the third hit on Google.

Benjamin Lim

but because of this US online privacy offensive a lot of links did not work

Matt N.

I don't like .djvu.

Oops. True! I wouldn't d/l that if I were you. Isn't Australia pretty strict?

Daniil

uh, copyfascists

Benjamin Lim

@MattN But so many people download like crazy here it's so hectic that no one really cares

Daniil

Use Tor if you are concerned about your safety

Kannappan Sampath

13:19

@MattN Why? That presumable occupies less space.

Matt N.

@KannappanSampath I don't like the software that I use to open and read them. I don't like pdf either. If I like something I get myself a paper copy.

Daniil

@BenjaminLim libgen.info/view.php?id=534538

If you have troubles downloading it, I can reupload it somewhere else

Benjamin Lim

spasiba

Daniil

:)

Benjamin Lim

I already have the file :D :D

Kannappan Sampath

13:21

@MattN It's pretty costly for people like us coming from the 3rd world, you should agree.

Daniil

Yeah, Amazon's prices on textbooks are wild.

Benjamin Lim

@Daniil Once I heard my supervisor saying to his wife on the phone: Yaneznayu paka, yaneznayu paka, yaneznayu, paka paka paka and he slammed the phone down!!

Matt N.

@Daniil You are awesome! It's in pdf! : )

Daniil

@MattN "Получить файл"

the yellowish one

Matt N.

Yes, just realised. I'd clicked it a while ago and nothing happened. Now it worked.

Thank you!

Daniil

13:23

@BenjaminLim haha, he was muttering "i don't know, bye, i don't know, bye..."

Benjamin Lim

@Daniil where are you now in lomonosov state?

I know that was why I laughed like hell because I understood what he was saying

and then halfway there was the word "b***t"

Daniil

Heh, it must be easy to get away with swearing in a foreign language :p

David Wheeler

i love the 4 squares theorem

Daniil

I live in Moscow, if that's what you mean

Benjamin Lim

@Daniil you go to lomonosov state uni?

my supervisor is from there

Daniil

13:25

sorry, I am not comfortable with talking about specific universities

t.b.

@DavidWheeler A friend of mine found a completely elementary one page proof of that. Unfortunately a very similar argument was published just two years earlier.

Matt N.

Yes. But that wasn't what I was saying.
Btw, I sent you some friendly insult. : )

Benjamin Lim

@Daniil horosho

David Wheeler

@tb do you have a link?

Matt N.

I should go and do some more stuff. Bbl

Benjamin Lim

13:32

bye guys i'm going too

Matt N.

@Daniil Thanks for the book : )

Benjamin Lim

@tb @KannappanSampath @MattN @Daniil thanks for the book bye

Kannappan Sampath

@BenjaminLim Bye Take care.

Daniil

Later, @BenjaminLim

t.b.

13:47

@DavidWheeler no, unfortunately not. I only have a paper copy.

David Wheeler

harrumph! well i shall sleep then. fine lot you all are!

i'll come back and torture you later. bring weapons.

Gigili

14:05

I'm armed and ready, give up your weapons of mass destruction.

I am unstoppable! There is no way that Time Fly can stop me... from running away, that is.

Temp-bye.

Dylan Moreland

14:25

I give up.

t.b.

@DylanMoreland at least you tried :)

Henning Makholm

I do not like the sound my under-desk server makes.

t.b.

Scary or just loud?

Henning Makholm

Loud. Wheezing. Grating.

Dylan Moreland

If certain people were unable to ask questions, it would not be the worst thing in the world.

t.b.

14:33

Well, they already are. I think I would be specific and say post instead of ask.

Henning Makholm

Okay, at least it's the CPU fan, not the hard drive...

t.b.

That's comforting...

At least somewhat.

Henning Makholm

Nothing a vacuum cleaner can'f fix ... i hope.

Runs nice and quiet after separating the fan from the heatsink and vacuuming between them. Now to see how it sounds after screwing it back in.

t.b.

crosses fingers

Henning Makholm

wheeze and grate again. Grumble.

t.b.

14:45

Is this moniker a euphemism for spambot?

Henning Makholm

If so, it's a rather erudite spambot, don't you think?

t.b.

:)

user19161

@KannappanSampath Sometimes I get the international paperback edition from say abebooks.com, you should check it out.

user19161

And check out 4shared.com, there is a lot of good stuff there in pdf and djvu form.

user19161

Shipping aside, other than special paperback versions, amazon.com is usually the cheapest.

t.b.

14:56

Speaking of spambots flag please!

Henning Makholm

15:07

Noise down from "angry 300-gram mosquito" to "slightly maladjusted idling Diesel engine" by taking out two of the attachment screws and making sure the power cabling leans against the fan case just so. Will have to do for now.

Daniil

@HenningMakholm can you recommend me some intro-level material on infinite trees and automata?

Henning Makholm

@Daniil Nothing definite comes to mind, sorry. I know there are such things as automata for infinite trees, but I've never sat down and studied them systematically.

Gigili

15:25

Have a minute @HenningMakholm?

Henning Makholm

Shoot.

Gigili

Should it be "could be transmitted from mother to fetus" or "can be transmitted blabla"?

Daniil

@HenningMakholm no worries, cheers

Henning Makholm

@Gigili Depends on what you're trying to say; "could" is more tentative than "can". If you say "can", it implies "this may or may not happen for you but we know there are some people it happens for", whereas "could" would imply "we don't actually know whether this ever happens, but we don't know that it doesn't happen either, so better be confused".

I don't think many native speakers would pick up on the difference unprompted, though -- but you'd have to ask one of them for that.

Gigili

@HenningMakholm Got it, thank you.

Very well explained.

t.b.

15:45

If anyone wonders who Dr. Terry Allen is: youtube.com/watch?v=Fgnx12iE3TU and arxiv.org/abs/1105.1383

Jonas Teuwen

I has improved theorem!

t.b.

Congratulations!

Jonas Teuwen

Yes 8-).

Hmm, I actually just made an inhomogeneous estimate homogeneous (which they say is a nicer result). But still, cool.

t.b.

Feels good, doesn't it? :)

Jonas Teuwen

Yeah.

t.b.

15:47

Now hit the Whisk(e)y in the Jar!

Jonas Teuwen

Surely will do that 8-).

Daniil

16:02

Arghh, why the fuck can't I concentrate on reading :|

This is bollocks, I am going for a small walk, before I go mad.

(sorry for pathetic blogging attempt)

Gigili

16:43

@Daniil Let me know if it works. So I can try it next time.

Matt N.

16:55

I'm working on an answer to this.

For $X=S^2$, I have $X/A$:

I thought maybe one can use that $X/A$ is path-connected and then compute $\pi_1 \cong H_1$ instead of doing $H_1$ directly.

But then I realised that I've never really computed a fundamental group so I can't finish my answer. Also, I'm not quite sure whether doing $\pi_1$ is actually easier than $H_1$.

Matt N.

17:10

Oh, that should've been $\pi_1^{ab} \cong H_1$.

@MattN Hello Matt. It might be easier to compute $H_1$ using cellular homology.

Too sleepy. Never mind.

Don't worry, you guys can come out now from behind the cupboards. I won't ask any more algebraic topology questions.

t.b.

17:37

climbs out of the box

Matt N.

: D

Hey does this mean that Dr. Terry Allen got his Dr. from Cornell?

Jonas Teuwen

No, it means that Cornell is the main sponsor of ArXiv.

Matt N.

Should look at the URL not the huge logo on the site : (

@JonasTeuwen Thanks : ) Now I feel quite stupid.

Jonas Teuwen

Don't be, I was wondering a similar thing some while ago.

t.b.

I don't think so. Genealogy doesn't know him either and if he got his Ph.D. (in maths) at an only mildly reputable uni in the past 50 years you can be pretty sure that he's in there.

Jonas Teuwen

17:44

But Genealogy doesn't know robjohn either, right?

I wouldn't call Princeton mildly reputable :-).

t.b.

And, moreover, he'd be pretty aware of the fact that posting something on ArXiV doesn't magically provide repuatbility of it

Henning Makholm

It doesn't know me, for example. Hopefully that's because the University of Copenhagen is more than mildly reputable.

Matt N.

: )

Jonas Teuwen

It doesn't know me either, but that's not so strange 8-).

Matt N.

It's a bit boring. It doesn't provide links to the actual theses.

Jonas Teuwen

17:47

This is my advisor.

Matt N.

It does know the Teddy, apparently.

Jonas Teuwen

So I will be the sixth.

Matt N.

Is this our guy?

t.b.

@HenningMakholm I was talking about the US.

Jonas Teuwen

Hmm, it seems to have the most Western-European universities too, no? :-).

But @HenningMakholm was in computer science, not mathematics, no?

Matt N.

17:50

I think the fact that I'm looking up this guy indicates that I'm bored.

Henning Makholm

@JonasTeuwen Sure, but it claims: Throughout this project when we use the word "mathematics" or "mathematician" we mean that word in a very inclusive sense. Thus, all relevant data from statistics, computer science, or operations research is welcome.

Matt N.

"is welcome" sounds as if they expect you to write your own entry.

Let's send Terry an email and tell him so he can write himself an entry there. : )

Jonas Teuwen

@HenningMakholm Sure, but they don't think it is very relevant?

Do people add themselves?

Gustavo Bandeira

Anyone read this:
http://www.amazon.com/The-Joy-Sets-Fundamentals-Undergraduate/dp/0387940944

?

t.b.

@JonasTeuwen More than what you ever wanted to know about it: ams.org/notices/200708/tx070801002p.pdf

Jonas Teuwen

18:01

@tb Hah, thanks.

Matt N.

@tb tl;dr -- did you add yourself or not?

t.b.

No. There was some librarian who was assigned from ETH to do this (I think).

At least there was lots of information that shouldn't have been there.

Jonas Teuwen

I like the title.

Matt N.

Not sure what you mean. I only mentions your two advisors. It would make sense to link to the thesis. No? That would much more interesting than someone's advisor.

Jonas Teuwen

Here we only get "dr.".

Kannappan Sampath

18:09

Missed that^ :/

Henning Makholm

@MattN Well, given that the entire purpose of the exercise is to model the student-advisor graph, your notion of "interesting" is abviously not what the project is using.

Matt N.

@KannappanSampath Don't worry it wasn't about you.

@HenningMakholm True dat. : )

t.b.

Is it just me or is it impossible to find Rajesh via this page?

(and if the latter is the case, why?)

Kannappan Sampath

@tb Because he probably has not participated much on Meta?

David Wheeler

@KannappanSampath hey are you there?

Kannappan Sampath

18:13

@DavidWheeler Sure, I am

David Wheeler

i have a weird request....if you can't help me, i totally understand

you're from india, right?

Matt N.

@tb He doesn't seem to have a meta account.

Kannappan Sampath

@DavidWheeler Yes.

@tb Forget it--He has asked 21 questions on Meta. :/

David Wheeler

ok, i'm looking for this song, see, and i have a bit of trouble since i can't recall much about it

Matt N.

@KannappanSampath Can you link to his meta profile?

Kannappan Sampath

18:16

@DavidWheeler Tell me something about it....

David Wheeler

this is what i know: it's a bhajan, i think done by MS Subbulakshmi

Kannappan Sampath

@MattN This

@DavidWheeler Is it Kurai Ondrum Illai, Kanna?

Matt N.

@KannappanSampath Weird. Thanks!

David Wheeler

well, see that's just it...i can't remember the name, and it's name was probably in another language anyway

and she's recorded like a gazillion records, too

Kannappan Sampath

Is it the one I linked?

David Wheeler

18:19

no...the record it's from was probably recorded in the early '80s i think

Gustavo Bandeira

Let a+b mean exactly that one of a, b is true. Express a+b in terms of the symbols introduced above. (Introduced symbols: And, Or, Not)

Is this the rioght answer? -> (a+b)&~(a&b)

Kannappan Sampath

@DavidWheeler Oh, so you're looking for a original rendition?

David Wheeler

one of the OTHER bhajans (not the one i'm looking for) was "he govinda he dayala" (or something like that)

and all i can remember is the LAST line, which isn't too helpful, because the name is usually the FIRST line

Kannappan Sampath

@DavidWheeler So, what is the last line?

Henning Makholm

@GustavoBandeira That + is not supposed to be a +, right?

David Wheeler

18:23

something like "hari nam kapyala" (probably spelled wrong)...i remember that the translation on the liner notes said it meant: hari is a name of god

Gustavo Bandeira

@HenningMakholm Nope, it means Or

@HenningMakholm Look here: turner.faculty.swau.edu/mathematics/materialslibrary/truth

David Wheeler

the first line was the same word (or phrase?) repeated over and over: something like: beelay, beelay, beelay

Henning Makholm

You can check your answer yourself by drawing up a truth table and checking that the overall value comes out as it should.

Gustavo Bandeira

Yup, i've done that.

And the truth values come up as i want.

Henning Makholm

Then that's your answer.

Gustavo Bandeira

18:25

I'm just unsure if that question is really asking what i answered.

David Wheeler

i suppose that's sort of like trying to find a beatles' song with the word "yeah" in it, but i have been looking quite hard....

anon

looks like + is disjunction and either # or (+) is exclusive or

Henning Makholm

@GustavoBandeira Looks right to me.

Gustavo Bandeira

Yay! I'm not so dumb (i guess)

Kannappan Sampath

@DavidWheeler Try this...

That satisfies Gazillion times record you mention...

Gustavo Bandeira

18:27

@HenningMakholm This is a print of the problem page: imm.io/lD0D

David Wheeler

perhaps i'm misreading it @GustavoBandeira, but i think you want: a+b <=> (avb)&~(a&b)

Gustavo Bandeira

<=> Iff?

David Wheeler

or in this case equivalent to

Gustavo Bandeira

@DavidWheeler Look the page print i sent: imm.io/lD0D

David Wheeler

your question asked you to define an equivalent expression for a+b....seems unfair to use + in the definition, no?

Henning Makholm

18:29

@GustavoBandeira Still looks alright. I'd have things to say about the author's pretending that the logical symbols are abbreviations for English words, but that's not your fault.

Gustavo Bandeira

@HenningMakholm Pretending? What you mean?

David Wheeler

i believe he is looking for the symmetric difference, and i used a "somewhat standard" v for logical "or"

Kannappan Sampath

@DavidWheeler Was that a wrong one too?

David Wheeler

the exclusive or: exactly one of a or b is true (one, or the other, but not both)

@KannappanSampath too long...this was just a short bhajan, maybe 5-6 minutes long

Kannappan Sampath

@DavidWheeler Oh, I see.

Gustavo Bandeira

18:33

@DavidWheeler The symmetric difference of OR is XOR?

David Wheeler

@GustavoBandeira yes

symmetric difference = xor

Kannappan Sampath

@DavidWheeler Did you find that from Youtube too?

Henning Makholm

@GustavoBandeira In reality the logical symbols have the precise, well-defined meanings you can read from their truth tables. There's nothing else needed to defined how they behave, though giving a rough equivalence to English words can sometimes help the intuition. However, it is important to be aware that the English words do not always behave like the logical symbols do, when used in ordinary English speech -- the meaning of English words are fuzzy, ambiguous, sometimes context-dependent...

David Wheeler

no, it's not on youtube

Gustavo Bandeira

@DavidWheeler XOR is the symetric difference or there is a symmetric difference for every boolean function?

Henning Makholm

18:35

... and the meaning of logical symbols are not. So attempting to define logical symbols as if they were just shorthand for English invites students to think that all of the inherent fuzziness in English expressions must also be present somehow in formal logic. That is a disservice.

David Wheeler

@HenningMakholm i answered the question Gustavo asked

Gustavo Bandeira

@HenningMakholm What you're telling me has something to do with this: en.wikipedia.org/wiki/Natural_semantic_metalanguage

David Wheeler

my "description" of it is informal, my symbology was not

Henning Makholm

@DavidWheeler I'm confused here. Suspecting crosstalk. I wasn't reacting to you.

Kannappan Sampath

@DavidWheeler OK. So, tell me about how you happent to listen to that song? Did you have a translation os some such?

t.b.

18:36

Thanks guys, I was distracted by expanding on my answer on meta (which was the reason for my asking)

David Wheeler

a friend of mine had the album

Gustavo Bandeira

@HenningMakholm Is it about that universal meanings?

Henning Makholm

@GustavoBandeira I don't think so.

Gustavo Bandeira

@HenningMakholm Yes, i've read the rest of your text. Thanks.

Kannappan Sampath

@DavidWheeler Then, I suggest you confirm if it's actually Subbulakshmi--BTW, why not ask him right away?

David Wheeler

18:39

@KannappanSampath geez, i have no idea where he is....this was...28 years ago?

Kannappan Sampath

@DavidWheeler !!!! Then, I'll try hard and see if I get lucky! :D

David Wheeler

@GustavoBandeira forgive me if i mis-interpreted your question, but it appears as if you were being asked to define a+b, and so + shouldn't occur in your definition (circularity)

Henning Makholm

@GustavoBandeira "Symmetric difference" is the one particular Boolean function you're trying to express. This name makes more sense when you consider naive set theory instead of truth values: then { x | (x in A) XOR (x in B) } is somehow the "difference" between the sets A and B, but it is symmetric in A and B in contrast to the ordinary set difference A \ B.

David Wheeler

i always think of logic in terms of sets, anyway...there's an isomorphism in there, somewhere

t.b.

there always is an isomorphism :) what do you mean?

Kannappan Sampath

18:44

@tb I have had 7 helpful posts and one not-helpful post! Is that a reason to be happy?

David Wheeler

the correlation between "natural" language and logical formalism really only breaks down with "or" because we use it linguistically to mean both XOR and OR

the other terms correspond fairly closely, a fact mathematicans use when writing proofs in words

Henning Makholm

It breaks down even more with "if" -- beginning textbooks in logic usually have to spend several pages telling how the English "if" does not always match how implication works.

t.b.

@KannappanSampath I guess so, I don't know. I wouldn't get worked up about it, but as long as you don't have more unhelpful posts, there's certainly no need to worry :)

Kannappan Sampath

@tb : ) I have decided not to get worked up with downvotes as well. It just renders my effort point less.

David Wheeler

but...but we still use "if" in proofs all the time. should we stop doing that?

Henning Makholm

18:48

Mathematicians have carefully conditioned themselves only to say "if" when in fact it matches the meaning of logical implication. The rest of the English-speaking world does not care and use "if" in a variety of other meanings (as do most mathematicians when they're not intending to express a mathematical claim).

David Wheeler

i do occasionally resort to the quaint-sounding terms "sufficient condition" and "necessary condition"

Henning Makholm

And there's nothing wrong with using "if" in this sense. It is just not the only one, and for a student who has not been carefully conditioned to the mathematical/logical "if", just giving that English translation for $\to$ is not going to help him understand it.

t.b.

@DavidWheeler I find that confusing: I always have to think about what implication is meant. Especially if somebody writes $A \iff B$. necessity: blah, blah sufficiency: blah blah.

Henning Makholm

Did we scare @Gustavo away?

David Wheeler

i've always found the term "only if" confusing, because of the logical meaning having a different parsing order than the written one

or is that "if", see now you've got ME confused....

m. k.

18:52

i just think in arrows

David Wheeler

it's "if"...that's just all wrong: we say A if B, but we read left-to-right, and the wrong synapses fire

m. k.

by replacing "if and only if" with "<=>" in my head

David Wheeler

i wonder sometimes about the ambiguity of language...do we think imprecisely, or did we just screw up when we invented language?

Kannappan Sampath

A if and only if is parsed as if - <=, only if- => Right?

Henning Makholm

@DavidWheeler It's only a screw-up if you think the reason for inventing language was so that we could do formal logic with it.

David Wheeler

18:56

well, didn't we KNOW we were going to invent mathematics? and if not, why not???

i talk to communicate...well, except for the occasional gazorninplat

m. k.

one caveman knew, but they beat him up with a rock when he started talking about ∃ and ∀

Daniil

@Gigili it did work a little bit :]

Hi, everyone.

Henning Makholm

In the immortal words of Geoffrey Pullum: Languages love multiple meanings. They lust after them. They roll around in them like a dog in fresh grass.

Matt N.

@HenningMakholm In reality it was a necessary development to keep the human race alive so it's been invented for the sole purpose of reproduction. So why abuse it to do formal logic? : )

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$Mathematics$ Mathematics