### Monday March 13, 2006, 4:00 PM

### tea at
3:40 PM at the Math Department lounge (Goldsmith 300)

**Speaker**: Stefan Friedl

**Title**: The Whitney trick and why
2 ⋅ 2
≰ 4 makes topology interesting

**Abstract**: The Whitney trick makes it possible to turn geometric problems into purely
algebraic problems. This trick only works in dimensions greater
than four. Four dimensional manifolds therefore show very different
phenomena than high dimensional manifolds.
I will use the problem of finding slice disks for knots to illustrate the
difference between high-dimensional manifolds and four dimensional
manifolds.