# COLLOQUIUM

## Introductory Algebraic K Theory and the Beauty of Mathematical Interconnections

### Fred Tinsley

Colorado College

**Friday April 23, 2010, 2:00 pm, in EMS E495A**

My initial venture into this subject began in the late 1970’s through my interest in geometric topology, in particular, in high dimensional surfaces or manifolds. Despite my geometric orientation, deep algebraic notions arising from the geometry and topology arose naturally. One of these was the Wall obstruction, arising during the detection of whether an open manifold is the interior of a compact manifold with boundary (Siebenmann). More recently, Craig Guilbault and I have encountered the same obstruction in our joint work.

Recently, two undergraduate students (Rahbar Virk and Yulan Qing) and I set out a single example of a commutative group ring for which the Wall obstruction is non-trivial. The result was a fascinating foray into commutative ring theory and algebraic number theory. I will talk about our experiences within the intersection of geometric topology, algebraic topology, commutative ring theory, and algebraic number theory.**Refreshments will be provided in EMS E495B at 1:30 pm.**

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