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Stream: event: MIT Categories Seminar

Topic: September 17: David Spivak's talk

Paolo Perrone (Sep 15 2020 at 14:44):

Hello all! This is the thread for David Spivak's talk, "Categories = polynomial comonads: a simple demonstration".

Paolo Perrone (Sep 15 2020 at 14:44):

When: Thursday, September 17th, 12 noon EDT (Boston time).

Paolo Perrone (Sep 15 2020 at 14:44):

Zoom meeting:
https://mit.zoom.us/j/280120646
Meeting ID: 280 120 646

Youtube live stream:
https://youtu.be/EIKraH4WwTM

Jacques Carette (Sep 15 2020 at 18:11):

Looks like the MIT ACT Seminar was part of the CT seminars, conferences & community events but this one isn't listed at https://teamup.com/ksfss6k4j1bxc8vztb
Not sure how to fix that, but that would be nice to do.

John Baez (Sep 15 2020 at 18:59):

I've always found the workings of the calendar mysterious! I don't know how to add new events, I don't know who to ask to do it, etc.

John Baez (Sep 15 2020 at 18:59):

Someone here will know.

John Baez (Sep 15 2020 at 19:00):

If there's a new series of talks at MIT, not on the calendar yet, someone please figure out how to add them to the calendar! And tell us how it works!

Nathanael Arkor (Sep 15 2020 at 19:06):

I can't tell what's going on: the TeamUp calendar is reading from the correct source, which does contain the new events, but they're not displaying on TeamUp for some reason.

Matteo Capucci (he/him) (Sep 16 2020 at 07:52):

John Baez said:

I've always found the workings of the calendar mysterious! I don't know how to add new events, I don't know who to ask to do it, etc.

You can ask me, I'm the admin, though admin links were posted here on Zulip too sometime ago

Matteo Capucci (he/him) (Sep 16 2020 at 07:53):

Screenshot-from-2020-09-16-09-52-34.png

Matteo Capucci (he/him) (Sep 16 2020 at 07:53):

I do see the event though

Matteo Capucci (he/him) (Sep 16 2020 at 07:54):

This topic was titled 'September 15: ...', that might have mislead some people. I corrected it.

Nathanael Arkor (Sep 16 2020 at 12:20):

It wasn't there yesterday, so perhaps TeamUp was just taking a little while to refresh.

Jacques Carette (Sep 16 2020 at 12:58):

I had to actually unsubscribe and re-subscribe (using Google Calendar) to get it to refresh. But it is there now.

John Baez (Sep 16 2020 at 18:18):

Thanks! Okay, I'll just remember this slogan: Calendar questions? Ask Matteo.

Matteo Capucci (he/him) (Sep 16 2020 at 20:28):

Nathanael Arkor said:

It wasn't there yesterday, so perhaps TeamUp was just taking a little while to refresh.

Yeah it syncs every ~3 hours, since MIT events are scraped from their own MIT calendar

Paolo Perrone (Sep 17 2020 at 15:45):

Hello all! We start in 15 minutes.

Jonas Frey (Sep 17 2020 at 16:40):

Hi! how can I find the youtube stream?

Paolo Perrone (Sep 17 2020 at 16:41):

https://youtu.be/EIKraH4WwTM

Jonas Frey (Sep 17 2020 at 16:44):

thanks!

Jonas Frey (Sep 17 2020 at 17:02):

this category of polynomials is the opposite of the small-coproduct-completion of Set, right? (this might be in Paige North's thesis)

Jonas Frey (Sep 17 2020 at 17:04):

that doesn't explain the monoidal product though ...

Brian Pinsky (Sep 17 2020 at 17:05):

There appears to be no nlab page for cofunctors. Can someone fix that? I feel like it's the sort of thing I'd want to be able to google.

Jonas Frey (Sep 17 2020 at 17:06):

small product completion

Jonas Frey (Sep 17 2020 at 17:06):

sorry

Brian Pinsky (Sep 17 2020 at 17:06):

Jonas Frey said:

this category of polynomials is the opposite of the small-coproduct-completion of Set, right? (this might be in Paige North's thesis)

Isn't set already small complete?

Jonas Frey (Sep 17 2020 at 17:07):

yes, but you can freely add small products again

Nathanael Arkor (Sep 17 2020 at 17:07):

The category of polynomials is given by $\mathbf{Cocart}(\mathbf{Cart}(1))$.

Brian Pinsky (Sep 17 2020 at 17:07):

Jonas Frey said:

yes, but you can freely add small products again

aah okay thanks

Jonas Frey (Sep 17 2020 at 17:08):

by cocart and cart you mean free sum completion and free coproduct completion?

Jonas Frey (Sep 17 2020 at 17:08):

that sounds right

Jonas Frey (Sep 17 2020 at 17:09):

thanks

Nathanael Arkor (Sep 17 2020 at 17:09):

Nathanael Arkor said:

The category of polynomials is given by $\mathbf{Cocart}(\mathbf{Cart}(1))$.

Equivalently, $\mathbf{Cocart}(\mathbf{Set}°)$, so $\mathbf{Cart}(\mathbf{Set})°$.

Nathanael Arkor (Sep 17 2020 at 17:09):

Jonas Frey said:

by cocart and cart you mean free sum completion and free coproduct completion?

Yes, free small coproducts and products.

Jonas Frey (Sep 17 2020 at 17:09):

yes

Jonas Frey (Sep 17 2020 at 17:28):

Jonas Frey said:

this category of polynomials is the opposite of the small-coproduct-completion of Set, right? (this might be in Paige North's thesis)

Correction: I thought of Tamara von Glehn's thesis https://www.repository.cam.ac.uk/handle/1810/254394

Paolo Perrone (Sep 17 2020 at 22:14):

Video here!
https://youtu.be/2mWnrgPIrlA