# #math

##### arxiv2bib– Jun 29, 2020 #math #arxiv

tl;dr: a2b.idrissi.eu to get a .bib from arXiv entries.

Have you ever wanted to create a bib entry from an arXiv preprint? There are a few tools available, including one provided by arXiv (click on “NASA ADS” in the sidebar when viewing an entry), but none of them worked as I wanted. They all had quirks and problems (like displaying some URL twice, putting “arXiv” as in the journal field even though it doesn’t belong there, no biblatex support, etc). In the end, I always had to fix things by hand, and it took almost as long as writing the entry myself.

##### Peccot lecture & COVID-19– Last updated on Jun 26, 2020 #math #peccot

Update: The videos are now available on Youtube! Please go there for the third lecture and there for the fourth lecture.

As some of you may know I was one of the people chosen this year to give a Peccot lecture at the Collège de France (see my first post about it). And as you all know for sure, normal life came to a halt a couple of months ago when the number of COVID-19 cases exploded in France (and the world) and the French government ordered a lockdown. While I was able to give my first two lectures before the lockdown started, the last two had to be postponed.

Thankfully, the number of cases is now diminishing and the lockdown is progressively being lifted. I was thus able to record my third lecture yesterday; it should appear online in a few days. The experience was somewhat surreal: I gave a two-hour lecture to a large classroom that was completely empty except for the cameraman and me. I had to give some online classes during the lockdown, but even then there was a certain sense of interactivity, whereas I was almost literally talking to wall yesterday, which was a bit destabilizing. But still, I’m happy that I was able to record the lecture, and I’d like to thank the Collège de France again for the opportunity! The current situation is extremely difficult for everyone, and I’m not the worst one off: it’s a very small sacrifice in the face of the public health crisis.

I hope people will still find it interesting and that the video will not feel too strange. I could not take questions during the lecture, obviously, but I will be happy to answer any you might have via email.

##### Braid video– Apr 21, 2020 #math #talk #animation

Thursday I’m giving a talk at the online Toric Topology research seminar. (I was supposed to go there in person, but you can probably expect, the current pandemic made that impossible.) So I took the opportunity to prepare a little illustration to explain the connection between braids and configuration spaces!

##### First Peccot lecture– Mar 5, 2020 #math #peccot

Yesterday was my first Peccot lecture! I think it went okay. The video is going to be available soon on this webpage. I mainly talked about the background for my course: what are configuration spaces, why do we care about them, what do we know about them, and what we would like to know about them.

##### Video– Feb 28, 2020 #math #peccot #animation

I am finishing to prepare my Peccot Lectures that start next week. I have prepared a small animation to illustrate the Fulton–MacPherson compactification using Blender, and I think it’s relatively neat! I am not a 3D artist, obviously, but (with oral explanations) I think it explains the concept better than drawing on the board, since drawing moving 3D pictures is not an easy task… The animation is available here, and here it is in all its glory:

##### Peccot Lecture– Sep 24, 2019 #math #peccot

Yesterday I received a letter from the Collège de France. I have been selected to give this year a Peccot Lecture, which “rewards each year young mathematicians under 30 who have been noticed in theoretical or applied mathematics” 😃. This is of course a great honor and I am very grateful! I still have to determine what the lecture will be about, but hopefully something about operads and configuration spaces. Together with my graduate course on homotopy theory, next semester will be interesting, teaching-wise!

##### Lecture Notes– Sep 11, 2019 #math #class

This summer I’ve started to compile lecture notes for my class on homotopy theory in January/February. They are heavily inspired by Grégory Ginot’s lecture notes from last year on the same subject, although I’ve reorganized them a bit; in particular I swapped the last two chapters. They are still missing the last chapter on $$\infty$$-categories, and they probably need a lot of polishing – I am mainly planning to use them as a memory aid during the lectures – but in case you are interested, they’re available here. If you take a look at them, don’t hesitate to let me know about any remarks you might have (typos, errors…)

##### A Model for Configuration Spaces of Closed Manifolds– Feb 24, 2017 #math #conf-spaces

Last week I was at the Max Planck Institute for the Conference for Young researchers in homotopy theory and categorical structures (which was, by the way, a great conference – thanks to the organizers), and I gave yet another talk about the Lambrechts–Stanley model for configuration spaces. So maybe it’s time I write a little bit about it on this blog. I’ll write a first post about the model itself, and later I will explain how the Fulton–MacPherson operad is involved in all this.

##### The Voronov Product of Operads– Sep 22, 2016 #math #operads #swiss-cheese

My first real post in a while! It turns out that writing an actual paper (cf. previous blog post) takes a lot of time and effort. Who knew?

The Voronov product of operads is an operation introduced by Voronov in his paper The Swiss-cheese operad (he just called it “the product”). It combines an operad and a multiplicative operad to yield a new colored operad; the main example I know is the homology of the Swiss-cheese operad. This is a construction that I use in my preprint Swiss-Cheese operad and Drinfeld center, where as far as I know I coined the name “Voronov product” – I haven’t seen this operation at all outside of Voronov’s paper. I wanted to advertise it a bit because I find it quite interesting and I’m eager to see what people can do with it.

The purpose of this post is to record the definition of $$\infty$$-operads and explain why it works like that. For this I’m using Lurie’s definition of $$\infty$$-operads; there is also a definition by Cisinski–Moerdijk–Weiss using dendroidal sets, about which I might talk later.

Indeed, the definition on an $$\infty$$-operad is a bit mysterious taken “as-is” – see [HA, §2.1.1.10]. My goal is to explain how to reach this definition, mostly for my own sake. Most of what follows is taken either from the book Higher Algebra, the $$n$$Lab, or the semester-long workshop about hgiher category theory in Lille in 2015.

##### List of Facts– Mar 31, 2016 #math

I just started a list of facts, mainly rather classical facts that I don’t want to forget. Before, that list lived on sheets of papers strewn across my desk, which was clearly not optimal. Now it’s in a more permanent form.

##### The Milnor–Moore Theorem– Mar 10, 2016 #math #algtop

This post is about the Milnor–Moore theorem, a powerful tool describing the structure of (co)commutative Hopf algebras. Like the Eckmann–Hilton argument, it shows that having multiple compatible operations on the same object can lead to unexpected results about the object. Briefly, the theorem says that as soon as the Hopf algebra is cocommutative and connected, then it is isomorphic to the universal enveloping algebra of a Lie algebra (and a similar dual statement is true for commutative Hopf algebras).

##### Acyclic Models– Jan 15, 2016 #math #algtop

The theorem(s) of acyclic models are a rather powerful technique for proving that some functors defined on truncated chain complexes can be extended in higher dimensions, and that two such functors are homotopic, by proving it on a small class of “model” objects.

For some reason I only discovered this last year, and I always find myself forgetting the precise hypotheses and conclusion… Hopefully writing this blog post will fix them in my mind. My main reference will be:

• Samuel Eilenberg and Saunders MacLane. “Acyclic models”. In: Amer. J. Math. 75 (1953), pp. 189–199. ISSN: 0002-9327. JSTOR: 2372628. MR0052766.
This post is about something somewhat weird I noticed about infinitesimal bimodules over operads and their relationships with some $$E_n$$ operads. I don’t know if it’s something significant, and I’d definitely be interested to hear more about it.