### Every other Wednesday, 4:30-6:30 p.m., SC 507 (with some exceptions).

Talk begins at 4:30, reception begins at 5:30, snacks provided.

**Next talk:**

### October 9

**Speaker:** Marius Lemm (Harvard)
**Title:** TBA
**Abstract:** TBA

**Past and Future Talks:**

### September 11

**Speaker:** Joe Harris (Harvard)
**Title:** How many lines meet each of 4 given lines in 3-space, and why it matters
**Abstract:** Basic linear algebra tells us how pairs of subspaces of a vector space can intersect. It says less about intersections of multiple subspaces. For example, given four 2-planes W_1, W_2, W_3 and W_4 of a four-dimensional vector space W, we can ask whether there are any 2-planes that have nonzero intersection with all four (the problem that translates into the question of the title).
In the late 19th century, Hermann Schubert developed a "calculus of conditions" to answer these questions. It's a beautiful theory, which is still an object of research today, but beyond that it's had an enormous impact on the development of geometry, for example inspiring Poincare to introduce the notions of cohomology and cup product. In this talk I'll give a very brief overview both of the Schubert calculus and the developments to which it gave rise.

### September 25 and 26, as part of the "Why do math?" series

**Speaker:** Francis Su (Harvey Mudd)
**Talk 1:** Mathematics for Human Flourishing
**Talk 2:** Sperner's lemma: topological combinatorics solving social science problems

### October 9

**Speaker:** Marius Lemm (Harvard)
**Title:** TBA
**Abstract:** TBA

### October 23

**Speaker:** TBA
**Title:** TBA
**Abstract:** TBA

### November 6

**Speaker:** TBA
**Title:** TBA
**Abstract:** TBA

### November 20

**Speaker:** Brooke Ullery (Harvard)
**Title:** TBA
**Abstract:** TBA

**Mailing list:** You can subscribe to the seminar mailing list here.

**Organizers:** Ana Balibanu (ana@math.harvard.edu) and Sebastien Picard (spicard@math.harvard.edu)