Zulip Chat Archive
Stream: mathlib4
Topic: Left vs right closed monoidal categories
Brendan Seamas Murphy (Feb 09 2024 at 21:35):
In the docstring for CategoryTheory.MonoidalClosed
it says that this is defining right monoidal closed categories. But the definition of right closed on wikipedia (and I think on the nlab, if I'm reading it right) would say we've defined a left closed category, because Closed X
carries the data of a right adjoint for the left tensoring X ⊗ -
. Is this a case where mathematical terminology is inconsistent, and some sources swap the meaning of left and right closed, or is it an error of the doc string?
Brendan Seamas Murphy (Feb 09 2024 at 21:35):
(I would like to implement separate left and right closed monoidal category classes, and it seems worth figuring this out first)
Johan Commelin (Feb 10 2024 at 04:18):
cc @Yuma Mizuno
Yuma Mizuno (Feb 10 2024 at 05:16):
I'm not sure which one (defined for X ⊗ -
or - ⊗ X
) should be called the left closed, but I think it's reasonable to change the current mathlib version to "left", which is at least consistent with Wikipedia.
Perhaps @Scott Morrison has some ideas?
Kim Morrison (Feb 10 2024 at 05:23):
I think I choose this name based on having the opposite reading of nlab than Brendan's. They call (- \otimes X) left tensoring. It is of course fairly arbitrary.
Brendan Seamas Murphy (Feb 10 2024 at 05:25):
Ah, on reread you're right. That is frustrating. I'm not sure what the right choice is, but I guess I don't like it if we use a convention based off (- \otimes X) meaning "left tensoring" when in mathlib tensorLeft X is X \otimes -
Kim Morrison (Feb 10 2024 at 05:29):
I'm pretty sure the literature is largely inconsistent here. Internal consistency will suffice for us.
Last updated: May 02 2025 at 03:31 UTC