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Atrium > Mathematics, Physics & Philosophy: category theory jokes (that do not use "co")

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  1.  
    • CommentRowNumber1.
    • CommentAuthorMike Shulman
    • CommentTimeNov 18th 2015
    • CommentRowNumber2.
    • CommentAuthorIngoBlechschmidt
    • CommentTimeNov 18th 2015
    • (edited Nov 18th 2015)

    This one is not directly about category theory, but rather sheaf theory. (I don’t have a Google+ account, feel free to relay if deemed sufficiently relevant and funny.)

    A sheaf and a presheaf are walking down the street. Suddently the presheaf spots the sheafification functor in the distance. “Quick! Hide! The sheafification functor is coming!”, warns the presheaf. The sheaf however stays calm and proudly explains, “I’m already a sheaf. The sheafification functor can’t harm me.” Eventually the sheafification functor arrives and reduces the sheaf to the terminal one. What happened? It was the sheafification functor with respect to the trivial topology where any family is regarded as a covering family.

    Edit: Not a joke, but arguably still funny (in allusion to the well-known phrase “right is where your thumb is on the left”): Right is where the tensor product is exact.

    • CommentRowNumber3.
    • CommentAuthorUrs
    • CommentTimeNov 19th 2015
    • (edited Nov 19th 2015)

    I find it funny that the annual Category Theory conference makes available only the abstracts of the contributed talks.

    • CommentRowNumber4.
    • CommentAuthorTobyBartels
    • CommentTimeNov 19th 2015

    I've heard the sheafification joke about e x\mathrm{e}^x and a constant function meeting a differential operator. (Punchline: it's ∂/∂y\partial/\partial{y}.) Both jokes, I suppose, are about the importance of not making assumptions about the context.

    • CommentRowNumber5.
    • CommentAuthorMike Shulman
    • CommentTimeNov 20th 2015

    I wonder if I could use that joke to explain to my calculus students why they shouldn’t write y′y'.

    • CommentRowNumber6.
    • CommentAuthorNikolajK
    • CommentTimeNov 21st 2015
    • (edited Nov 21st 2015)

    Once I was thinking what the category of my ex-girlfriends should be. Then I realized I was treating women as objects.

    (And then I realized that this would pass as a punch line.)

    • CommentRowNumber7.
    • CommentAuthorTodd_Trimble
    • CommentTimeNov 21st 2015

    That’s a really good one, Nikolaj!

  8. I learned the following play of words from Yuri Sulyma (at the previous week’s Topos à l’IHES):

    Let 𝒞\mathcal{C} be a category. Let X,Y∈𝒞X,Y \in \mathcal{C} be objects. Assume that the induced representable presheaves Hom(⋅,X)Hom(\cdot,X) and Hom(⋅,Y)Hom(\cdot,Y) are naturally isomorphic. Then how do you prove that XX and YY are themselves isomorphic? Yo ned a lemma for that.

    • CommentRowNumber9.
    • CommentAuthorPaoloPerrone
    • CommentTimeOct 13th 2016
    A 2-mathematician is a mapping between two ways of turning coffee into theorems.

  10. I’ve learned this one from Ingo Blechschmidt while on a walk through a forest at night in october of 2019, back when I first got into category theory. When I laughed, he called it the best reaction he got yet.

    What does a category theorist say during meditation? Hooooommmm

1 to 10 of 10

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