Hacker News new | past | comments | ask | show | jobs | submit login

"Categorical set theory" > "References" https://en.wikipedia.org/wiki/Categorical_set_theory#Referen...

From "Homotopy category" > "Concrete categories" https://en.wikipedia.org/wiki/Homotopy_category#Concrete_cat... :

> While the objects of a homotopy category are sets (with additional structure), the morphisms are not actual functions between them, but rather a classes of functions (in the naive homotopy category) or "zigzags" of functions (in the homotopy category). Indeed, Freyd showed that neither the naive homotopy category of pointed spaces nor the homotopy category of pointed spaces is a concrete category. That is, there is no faithful functor from these categories to the category of sets.

My "understanding" of category theory is extremely shallow, but that's exactly why I think my proposal makes sense. It is the kind of thing that everybody ignores for decades precisely because it's transparently obvious, like a fish that doesn't understand water.

Here is the statement:

The meaning of no category is every category.

reference: https://terrytao.wordpress.com/2008/02/05/the-blue-eyed-isla...

This was already understood by everybody in the field, no doubt. It's just that somebody has to actually say it to someone else in order for the symmetry to break. The link above has the exact description of this, from Terence Tao.

Guidelines | FAQ | Support | API | Security | Lists | Bookmarklet | Legal | Apply to YC | Contact