# Abigail Thompson

**Regular Faculty****Topology**

Ph.D., 1986, Rutgers University**Refereed publications:** Via Math Reviews

**Web Page: ** http://www.math.ucdavis.edu/~thompson/

Email: thompson@math.ucdavis.edu

Office: MSB 2220

Phone: 601-4444 x4002

Professor Abigail Thompson studies combinatorial methods in 3-dimensional topology. Despite the recent influence of algebraic and geometric techniques such as quantum groups, hyperbolic geometry, and algebraic varieties in the study of 3-manifolds, most of the fundamental arguments involve or can be reduced to cutting and pasting surfaces and manifolds and studying their possible combinatorial configurations. Knots and links are an especially good starting point for such reasoning, both because complements are representative examples of 3-manifolds, and because the knots and links in a 3-manifold are a fundamental part of its structure.

In joint work with Scharlemann, Professor Thompson has obtained a number of new
classification and decision results and new
proofs of old results using an important cut-and-paste concept called thin
position. In particular, she has found a simplified argument that an
algorithm of Rubinstein decides if a particular 3-manifold is
homeomorphic to S^3 **[5]**. She and Scharlemann also gave a
much simpler proof of Waldhausen's theorem **[4]**, which states that there is only
one Heegaard splitting of the 3-sphere of each genus. This work
has the following two consequences, among others. First, it relates primitive
descriptions of 3-manifolds, such as triangulations and Heegaard
splittings, to their deep instrinsic structure, and it may lead to
generalizations such as an algorithm to decide if any two 3-manifolds are
homeomorphic. Second, it is progress towards the
Poincaré conjecture. For example, if one is
presented with a 3-manifold and happens to know that it is simply-connected,
Rubinstein's algorithm is a way to conclusively determine whether or not it is
a counterample to Poincaré.

Professor Thompson also showed that all knots which are band-connected
sums have Property P, meaning that Dehn surgery on such a knot cannot
produce a counterexample to the conjecture **[1]**. Since band-connected sums do
not appear to be fundamentally simpler than other types of knots, this result
is good evidence that all knots have Property P, which in turn is an important
special case of the Poincaré conjecture.

### Selected publications

**[1]**Property P for the band-connect sum of two knots, Topology 26 (1987), 205-207.

**[2]** Link genus and the Conway moves (with M. Scharlemann), Comment. Math. Helv.
64 (1989), 527-535.

**[3]** Detecting unknotted graphs in 3-space (with M. Scharlemann), J.
Differential Geom. 34 (1991), 539-560.

**[4]** Thin position and Heegaard splittings of the 3-sphere (with M.
Scharlemann), J. Differential Geom. 39 (1994), 343-357.

**[5]** Thin position and Rubinstein's solution to the recognition problem for S3,
Math. Res. Lett. 1 (1994), 613-630.

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