# Do good math jokes exist? [closed]

Have a good joke? Share.

I know this is subjective, but the principle "should be of interest to mathematicians" trumps. (I hope.)

## closed as off topic by S. Carnahan♦, Scott Morrison♦Dec 24 '09 at 2:21

Questions on MathOverflow are expected to relate to research level mathematics within the scope defined by the community. Consider editing the question or leaving comments for improvement if you believe the question can be reworded to fit within the scope. Read more about reopening questions here. If this question can be reworded to fit the rules in the help center, please edit the question.

## locked by S. Carnahan♦Sep 2 at 3:09

This question exists because it has historical significance, but it is not considered a good, on-topic question for this site, so please do not use it as evidence that you can ask similar questions here. This question and its answers are frozen and cannot be changed. More info: help center.

• I just voted this -1, and I'd like to see the question closed. People have had over a month to enjoy it, and its continued presence on the front page seems to encourage people to post very soft questions. This takes Math Overflow in what I think is a bad direction. – Tom Leinster Nov 28 '09 at 12:34
• I disagree with Tom. I think some levity is desirable, and MO shouldn't all be serious business. – Richard Dore Dec 10 '09 at 21:50
• With respect to the title, "No." – Harry Gindi Dec 10 '09 at 22:23
• I've decided to finally put this one out of its misery. All that's happening now is people add new, mostly lame, jokes at the the end, which no one ever reads, and as a result the question keeps bouncing back to the front page. It's time to die. Closed. – Scott Morrison Dec 24 '09 at 2:23
• The Pigeonhole Principle: If there are n pigeons and n+1 holes, then at least one pigeon must have at least two holes in it. – Bhaskar Vashishth May 6 '15 at 2:32

Mathematician1: So why did you become a mathematician?

Mathematician2: I don't like working with numbers.

• Mathematician 2's reply makes sense for differential geometers, topologists, category theorists, e.t.c. – user62675 Mar 26 '14 at 0:43

Here are some of my favorites that were invented by friends of mine:

Q: What kind of maps should you take with you on car trips?

A: Automorphisms.

Q: What do you call it when you're trying to prove that a map is injective, but you just can't do it?

A: Monic fail.

• I couldn't, for the life of me, figure out how automorphisms were supposed to be useful on car trips. After all, it doesn't really help to show that the landscape outside your window is non-trivially equivalent to itself; what you're really interested in is showing that it's equivalent to some smaller object you have within your vehicle. Then I realized it's a pun. – Tanner Swett Jan 12 '11 at 13:05

Do good math jokes exist? Under the axiom of choice, sure. But it's not possible to find an explicit example.

An engineer hears that a famous mathematician will be giving a public lecture, and always having a soft spot for math, he attends. The mathematician then talks at length about all sorts of amazing phenomena that happen in 17 dimensional space. The engineer, amazed at this mathematician's intuition for 17 dimensional space, goes up to him afterwards and asks 'How do you picture 17 dimensions?", to which the mathematician answers 'Oh, its easy. Just imagine n-dimensional space, and set n equal to 17.'

My dad (an engineer) loves that joke.

What did the forgetful functor do for his stoner friend?

He left adjoint as a free object.

After introducing general topological spaces, the professor began to introduce the notion of convergence without a metric. He turned around and said,

"I have no balls."

A hit for months.

• Hmm, P.M.´s lecture on Functional Analysis? – M.G. Jun 19 '10 at 17:10
• It's classical. Like the professor saying that "$\mathbb{R}^n$ has got balls" – Qfwfq Dec 5 '12 at 15:15

Q: What's purple and commutes? A: A dead baby in a suitcase.

Q: What's purple and commutes and has a certain number of followers? A: A dead baby Jesus in a suitcase.

• Excellent! Only a mathematician would get this! – Steven Gubkin Mar 5 '10 at 18:08
• a mix of math jokes with dead babies, and they said it could'nt be done... – Sean Tilson Mar 6 '10 at 1:19
• I don't get this one... could someone please explain? – finitud Dec 11 '13 at 15:52
• @finitud The first is a play on a very common joke about a different meaning of "commutes": mathoverflow.net/a/1205/28209 – Mark S. Dec 30 '13 at 3:03

There are 10 types of people in the world: those who understand binary, and 9 others.

• From a lecture in grad school years ago: There are three kinds of people in the world: those who can count and those who cannot. – José Figueroa-O'Farrill Oct 27 '09 at 10:22

Less of a joke than an observation, but...

I've always found it appropriate that online identity thieves are in the business of stealing ones and zeroes.

• Ha! I only got this on my third readthrough of this list. – Cam McLeman Apr 26 '10 at 14:23
• I still don't get this... – Qiaochu Yuan Jun 10 '10 at 12:20
• @Qiaochu Yuan: One and zero are identities. :-) – shreevatsa Jul 8 '10 at 4:34
• Bwahaha! I like this one... :) – rschwieb Jun 26 '12 at 14:57

The water receded and the Ark came to rest upon the land. Noah opened the doors and commanded the animals, “Go forth and multiply.” The animals slowly departed the Ark except for two snakes that remained in the back. Again Noah proclaimed ,“Go forth and multiply” yet the two snakes did not move. Noah walked to the back of the Arc and asked, “Why have you not followed my command”.? The snakes answered, “Noah, we can’t because we are Adders.”

Noah then went out upon the land and felled several large trees; from these trees he made a four legged platform. He then went inside the Arc and carried the snakes outside and upon placing them on the platform, his words became true.

As everyone knows … Adders can multiply using log tables.

• A beautiful cringe – galois May 2 '16 at 19:51

Perhaps the question should be, not "Do good math jokes exist", but "are they unique"?

• I think there's only one isomorphism class of math joke. – userN Oct 19 '09 at 15:48
• But sadly, it has non-trivial automorphisms. – Andrew Critch Dec 1 '09 at 10:42
• Let's classify the category of math jokes. Is it additive? abelian? triangulated? tannakian? a topos? – David Corwin Dec 28 '12 at 6:25

One of my favorites. It's about a statistician - close enough for me. (I found this version of the joke here)

A physicist, an engineer, and a statistician were out game hunting. The engineer spied a bear in the distance, so they got a little closer. "Let me take the first shot!" said the engineer, who missed the bear by three metres to the left. "You're incompetent! Let me try" insisted the physicist, who then proceeded to miss by three metres to the right. "Ooh, we got him!!" said the statistician.

My favourite is supposedly a joke made by a mathematician who was interviewing a not very good graduate student who was taking generals. The interview was going badly, so to make the student feel better the mathematician asked him for an example of a compact topological space. "The reals?" suggested the student, to which the mathematician replied, "Which topology were you taking?"

• I heard this one, and with the names of those involved, but slightly differently: there were two examiners and, in desperation, one asked for an example of a compact space to which the answer "the reals" was offered. The second examiner, in a vain attempt to help, then asked "In what topology?". – Loop Space Oct 26 '09 at 7:33
• This might be apocryphal, but someone I know claims to have seen the paper. In a Topology exam, a question asked whether two spaces X and Y (defined in the question) were homeomorphic. One student answered: "X is, but Y isn't." – José Figueroa-O'Farrill Oct 27 '09 at 10:27
• Some years ago, David Letterman had a series of segments called "Over Our Heads" where he invited experts in various technical disciplines to come on and tell specialized jokes. Mike Roth (now a professor at Queens) knew one of the writers and was invited to tell a math joke. Andrew's version of the oral exam/topology of the reals joke is the one he told. Andrew's version of the – D. Savitt Nov 6 '09 at 20:43
• Approximately two and a half years later I see that I didn't write what I intended to write. I did of course intend to write "compact" -- or else the joke makes no sense. In other words, Andrew Stacey's version is what I intended (except that in my version there was just one examiner). – gowers Mar 23 '12 at 20:36
• Few years ago I failed a linear algebra student which replied to my question: "What is the dimension of the plane?" with "Infinity?". Only after she had left I realized I should had asked her: "Over which field?" – Vít Tuček Jun 22 '16 at 12:53

I find the observation that the grade school carry operation from addition-with-carry forms a non-trivial degree 1 cocycle in the group cohomology of Z/10 a pretty good joke embedded in mathematics.

• I really don't get the non-mathematical part of this joke. What is "the grade school carry operation from addition-with-carry"? – jmc Feb 20 '15 at 21:15
• @jmc It's the digit you carry when adding two decimal digits $a, b$: $c(a, b) = 0$ if $a + b < 10$, and $c(a, b) = 1$ if $a + b \geq 10$. This $c: \mathbb{Z}/10 \times \mathbb{Z}/10 \to \mathbb{Z}/10$ is a 2-cocycle representing an element in $H^2(\mathbb{Z}/10, \mathbb{Z}/10)$ that classifies the extension $0 \to \mathbb{Z}/10 \to \mathbb{Z}/100 \to \mathbb{Z}/10 \to 0$. See ncatlab.org/nlab/show/carrying for more. – Todd Trimble Jan 2 '16 at 22:46

I also find the book Mathematics Made Difficult by Linderholm to be hilarious. I'm not going to search for favorites, but I find the first 2 exercises amusing:

"1. Show that a finite subset of an arbitrary set E in a ring suffices to generate the ideal generated by E if, and only if, the ring is Noetherian.

*2. Show that 17 x 17 = 289. Generalize this result."

• Jonas, what is the answer to the second one? – Unknown Jun 12 '10 at 19:45
• I should have mentioned that the asterisk on the second problem is to indicate that it is especially difficult. I'm afraid I have not yet solved it. – Jonas Meyer Jun 15 '10 at 3:59
• @Unknown I think he's getting at the pattern in the digits. – Alephnull Aug 8 '16 at 21:14

A swiftie. Most of you are probably too young to remember them...

" $s = \displaystyle\int_a^b \sqrt{1 + [f'(x)]^2}\mathrm{d}x$ ", said Tom at length.

• Swifties were (and still are) published in the jokes section of "Boy's Life" (the official magazine for the Boy Scouts of America). I'm fairly young, but I know what they are! :) – apnorton Aug 22 '14 at 2:53

There's a Notices article on this.

• The jokes in that article are terrible, though. – Qiaochu Yuan Oct 18 '09 at 22:04
• @Qiaochu: But the article itself is kind of hilarious. – Harrison Brown Oct 18 '09 at 22:09
• I read the article two years ago, it is fun. Considering that maths is a culture, we need this sort of ingredient. – Sunni Mar 6 '10 at 17:26

An excerpt from H. Petard, "A contribution to the mathematical theory of big game hunting," The American Mathematical Monthly, vol. 45, no. 7, pp. 446-447, 1938:

The Hilbert, or axiomatic, method. We place a locked cage at a given point of the desert. We then introduce the following logical system.

• Axiom I. The class of lions in the Sahara Desert is non-void.
• Axiom II. If there is a lion in the Sahara Desert, there is a lion in the cage.
• Rule of Procedure. If p is a theorem, and "p implies q" is a theorem, then q is a theorem.
• Theorem I. There is a lion in the cage.

The method of inversive geometry. We place a spherical cage in the desert, enter it, and lock it. We perform an inversion with respect to the cage. The lion is then in the interior of the cage, and we are outside.

The method of projective geometry. Without loss of generality, we may regard the Sahara Desert as a plane. Project the plane into a line, and then project the line into an interior point of the cage. The lion is projected into the same point.

The Bolzano-Weierstrass method. Bisect the desert by a line running N-S. The lion is either in the E portion or in the W portion; let us suppose him to be in the W portion. Bisect this portion by a line running E-W. The lion is either in the N portion or in the S portion; let us suppose him to be in the N portion. We continue this process indefinitely, constructing a sufficiently strong fence about the chosen portion at each step. The diameter of the chosen portions approaches zero, so that the lion is ultimately surrounded by a fence of arbitrarily small perimeter.

• <a href="gap-system.org/~history/Extras/Spitzer_lion.html">Full text of that paper</a> for those who don't have JSTOR access. – Michael Lugo Oct 19 '09 at 0:49
• I have replaced the JSTOR link with Michael's link. – las3rjock Oct 19 '09 at 1:09
• It's hard to beat the following for simplicity (or agreement with mathematical practice): go into the cage, lock it, and declare yourself to be on the outside. – Hugh Thomas Oct 19 '09 at 17:11
• Yeah, the method of inversive geometry is one of my favorites. – las3rjock Oct 19 '09 at 19:37

It was proven by Cantor that a good math joke exists. Unfortunately, his proof was entirely non-constructive.

• The earlier answer mathoverflow.net/a/1932/5340 already tells this... unless you know of a proof that works in ZF. – Zsbán Ambrus Jul 17 '14 at 17:23
• I have discovered a truly marvelous math joke that this comment box is too narrow to contain. – tilper Jun 6 '16 at 17:53

The continuous functions are having a ball. At the dance floor, cosine and sine are jumping up and down, and the polynomials are forming a ring. But the exponential function is standing separately the whole evening. Due to sympathy for it, the identity joins it and suggest: "Come one, just integrate yourself!" – "I've tried that already", answers the exponential function, "but it didn't change a bit!"

another one

Why the mathematician named his dog "Cauchy"? Because he leaves a residue at every pole

• Oh come on! mathoverflow.net/a/2254/5340 already has the Cauchy joke. – Zsbán Ambrus Jul 17 '14 at 17:24
• @ZsbánAmbrus and the link in the very first answer already had it before that. Do you really expect everyone to read every answer before posting their own? – tilper Jun 6 '16 at 17:55
• @tipler: no, but I expect you to at least do a text search in all posts for the obvious keywords like "Cauchy". – Zsbán Ambrus Sep 17 '16 at 5:04

Tom Lehrer was a Mathematician and this comes through in several of his famous skits. Not precisely a "math joke", but still mathy and pretty darn funny.

• Tom Lehrer was a genious. His song "Werner von Braun" is absolutely brilliant. – GMRA Oct 18 '09 at 23:58
• I hope Tom Lehrer still is a genius - I believe he's still alive :-) and yes, that's absolutely true. His wordplay and clever humor are really masterful. – Alon Amit Oct 19 '09 at 2:11
• I didn't know he was a mathematician! :) – Vectornaut Nov 29 '09 at 15:30
• He was my calculus section man in 1960 and apparently a democrat, since he proposed as an example of proof by vacuous hypothesis the statement: "all progressive republicans wear green eyeshades". – roy smith Sep 1 '11 at 16:09

A friend made this up recently (I prefer the first half on its own):

"No meal is complete without soup. But you have to order it first."

Also I like this meta-joke, also by a friend (who didn't understand the original):

"What's purple and commutes? An abelian eggplant."

EDIT: one more, by Elizabeth: "Does this Hausdorff measure make me look fat?"

A millionaire is trying to scientifically develop the best racing horse. He asked a biologist, veterinary, trainer, and a mathematician. The biologist gives him an advice about which type of horse to cross with which other type, the veterinary advices on how to feed the horse, and how to keep him healthy, the trainer explains how to physically train the horse. The mathematician does not reply. After a few weeks the millionaire meets the mathematician and it looks that the mathematician did not sleep much in recent days. Do you have a solution for me, ask the millionaire? It is a difficult problem, answers the mathematician, but I think I have a satisfactory solution to the case of spherical horses.

• The version I know of this joke has a physicist proposing a solution for spherical horses. The mathematician thinks long and hard, and announces that she has solved the problem: she can prove that, for every horse race, there exists a unique winner. – Nate Eldredge Nov 30 '10 at 16:49

Kurd Lasswitz, mathematician, writer, inventor of science fiction in Germany, wrote this "nth part of Faust" for the Breslau Mathematical Society 1882:

"Personen:
Prost, Stud. math. in höheren Semestern, steht vor dem Staats-Examen,
Mephisto, Dx (sprich De-ix), Differentialgeisterkönig, ein Fuchs.
Ort Breslau. Zeit: Nach dem Abendessen. (Rechts ein Sofa, auf dem Tische zwischen allerlei Büchern ein Bierseidel und Bierflaschen, links eine Tafel auf einem Gestell, Kreide und Schwamm. Auf der Tafel ist eine die gesamt Fläche einnehmende ungeheuerliche Differentialgleichung aufgeschrieben).

Prost am Tische, mit den Büchern beschäftigt. Er stärkt sich.

Prost

Habe nun, ach, Geometrie, Analysis und Algebra
und leider auch Zahlentheorie studiert,
und wie, das weiß man ja!
Da steh' ich nun als Kandidat
und finde zur Arbeit keinen Rat.
Ließe mich gern Herr Doktor lästern;
zieh' ich doch schon seit zwölf Semestern
herauf, herab und quer und krumm
meine Zeichen auf dem Papiere herum,
und seh', daß wir nichts integrieren können.
Es ist wahrhaftig zum Kopfeinrennen.

Zwar bin ich nicht so hirnverbrannt,
daß ich mich quälte als Pedant,
wenn ich 'ne Reihe potenziere,
zu seh'n, ob sie auch konvergiere,
... "

What did the zero say to the eight? "Nice belt."

• This joke isn't a math joke; it contains numbers. – user29225 Aug 10 '15 at 11:37
• @user29225 What did $S^1$ say to $S^1 \vee S^1$? "Nice belt." – Andres Mejia May 16 '16 at 19:36

I excuse my english if you spot some flaws...., since this is my first post here I thought it would be nice to share some neat jokes.

1) A mathematician, a physicist and an engineer were out in the countryside when they met a farmer trying to build a fence. They introduced themselves and the farmer asked them if they could help him shape the fence so he would get as much space as possible within it. The engineer stepped forward and said, that it would be best for the farmer to make the fence square, that would be easiest. The physicist then said that it would be better to make it as a circle, because then he would get as much space as possible. The mathematician laughed and said that you can get a lot more space then that! He took some pieces of fence and rolled it around himself, then he defined himself outside the fence!

2) Infinitely many mathematicians walked into a bar, the first one asked for one beer, the next one asked for half a beer, the third one asked for a quarter of a beer and the fourth one asked for one eight of a beer, then the bartender said :"screw this" and filled two glasses of beer!

3) An engineer was working on a problem when suddenly his trash bin caught fire. He immediately grabbed the fire extinguisher and put out the fire. In the next room a physicist was also working on a problem when his trash caught fire, he thought, fire extinguisher block oxygen from the fire, ergo fire is put out. So he grabs the fire extinguisher and puts out the fire. In the third room there was a mathematician working on a problem, his trash bin also caught fire so he looked at and thought, problem has a solution, and continued working!

• For the second joke, it's even better if the bartender says "you need to learn your limits!" – ಠ_ಠ Apr 18 '15 at 11:15

He had to work it with a pencil.

• I guess it's not for everyone - but it's my favorite math joke. – user891 Dec 10 '09 at 18:29

If somebody likes mathematical logic, category theory, lambda calculus, combinatory logic, then the following article can provide him/her jokes that are at the same time correct mathematical theorems:

Ruehr, Fritz (2001). The Evolution of a Haskell Programmer. Willamette University.

The article provides approaches to implement a mere Fibonacci function with such "over-calibrated" methods like harnessing deep metamathematical theorems (combinatory logic, category theory).

Haskell is a programming language (named after the logician Haskell B. Curry). It has been developed by academia (not by industry or market), and most motivations behind its creation was cleanness and purity. And it is based directly on lambda calculus, type theory, combinatory logic. Many of the programmer practice in it is based on category theory and algebra.

I once ad-libbed this one. (Alas, it is a late entrant.)

Q: Why is it important to study Verma modules of Lie algebras?

A: The most widely used modules of Lie algebras and Lie groups are finite-dimensional irreducible representations, the Weyl modules. Of course, you should learn them first when you study representation theory. But they are only the tip of the iceberg.

• Care to explain the joke to non-specialists? – Boris Bukh Nov 13 '09 at 9:39
• If you draw a highest-weight Verma module containing a finite-dimensional representation, e.g. for su(3), it is an infinite iceberg with a finite tip. I suppose that the joke is obscure, even for more most mathematicians. – Greg Kuperberg Nov 13 '09 at 15:04

A creation of my own:

Q:What did the simplicial set say to the fibrant replacement functor?

A:"Oh, I'm so horny..."