# Fukaya Categories of Surfaces, Math 595 FSC, Fall 2022

## Course description

The Fukaya category is a sophisticated invariant of symplectic manifolds whose definition in full generality is intricate. In the original formulation, objects of this category are certain “branes” supported on Lagrangian submanifolds, and the composition laws in the category involve pseudo-holomorphic maps with Lagrangian boundary conditions (Floer theory).

At the same time, a category, like any other algebraic structure, can admit many presentations. For instance, we could try to find a presentation of the Fukaya category by generators and relations, or we could try to build the Fukaya category of a symplectic manifold up from categories associated to smaller pieces of the manifold.

Let $$S$$ be a oriented surface (2-dimensional real manifold). The Fukaya category of $$S$$ is now well-understood enough that we know multiple ways of presenting it. The goal of this course is to study the Fukaya category of $$S$$ via multiple presentations, the original Floer theoretic definition being only one of them. Others include the theory of “gentle algebras” (by results of Haiden-Katzarkov-Kontsevich), and a perspective that views the Fukaya category of $$S$$ as an object in homological algebra (Dyckerhoff-Kapranov).

Thus, although this course will include some Floer theory, it will not be strictly speaking necessary in order to understand all of the different approaches to the Fukaya category of a surface. My hope is that students with different backgrounds in geometry and algebra will be able to find at least one way of thinking about the Fukaya category that makes sense to them. Applications of these ideas to Homological Mirror Symmetry will also be discussed.

• Prerequisites: Some familiarity with the tools of algebraic topology is strongly recommended.

## References

• DG categories
• $$A_\infty$$ categories
• Associahedra and moduli spaces of disks
• P. Seidel, Fukaya Categories and Picard-Lefschetz Theory, Chapter II, Section 9.
• Related: T. A. Driscoll and L. N. Trefethen, Schwarz-Christoffel Mappings.
• Gradings and signs on surfaces
• P. Seidel, Fukaya Categories and Picard-Lefschetz Theory, Chapter II, Section 13.
• Formal enlargements
• P. Seidel, Fukaya Categories and Picard-Lefschetz Theory, Chapter I.