I gave a talk last week in the Geometry, Analysis and Physics seminar with the title “The limit operator symbol”. This was an attempt to distill some of the ideas from my series of posts on the Lindner-Seidel and Spakula-Willett papers, especially post IV of the series. In particular, I wanted to explain the crucial move from having a series of inequalities *witnessed* to having a similar series of inequalities *centrally witnessed*. As Nigel put it during the seminar, we are attempting to describe a “witness (re)location program”: our witnesses are scattered all over \(\Gamma\), and we are attempting to move them all to the “courthouse”, that is, to a neighborhood of the identity, at the same time. Continue reading

# Category Archives: My Talks

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# What is noncommutative geometry?

I’m giving an introductory seminar talk this afternoon to let new graduate students know about the noncommutative geometry research group at Penn State and what it is we do. My plan is to begin with a short “elevator speech” about NCG (a few minutes) and then follow it up with four ten-minute vignettes of “Things we talk about a lot”

- Hilbert space
- K-theory
- Curvature
- Expanders

and at least to indicate the existence of all of the \( (4 \times 3)/2 = 6 \) connections among these concepts as well. Here is a link to a scanned version of my notes for the talk.

# My talk at BIRS

# Lectures on Coarse Index Theory at Fudan

### Here are the slides from a lecture series on “Coarse Index Theory” which I gave at Fudan University, in Shanghai, in May 2006

- Lecture 1: Elliptic Operators and K-Theory
- Lecture 2: Large Scale Indices
- Lecture 3: K-Theory Calculations
- Lecture 4: The Assembly Map
- Lecture 5: Equivariant Assembly