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# Mathematical Research Letters

## Volume 26 (2019)

### Number 2

### Trisections of $4$-manifolds via Lefschetz fibrations

Pages: 383 – 420

DOI: https://dx.doi.org/10.4310/MRL.2019.v26.n2.a3

#### Authors

#### Abstract

We develop a technique for gluing relative trisection diagrams of $4$-manifolds with nonempty connected boundary to obtain trisection diagrams for closed $4$-manifolds. As an application, we describe a trisection of any closed $4$-manifold which admits a Lefschetz fibration over $S^2$ equipped with a section of square $-1$, by an explicit diagram determined by the vanishing cycles of the Lefschetz fibration. In particular, we obtain a trisection diagram for some simply connected minimal complex surface of general type. As a consequence, we obtain explicit trisection diagrams for a pair of closed $4$-manifolds which are homeomorphic but not diffeomorphic. Moreover, we describe a trisection for any oriented $S^2$-bundle over any closed surface and in particular we draw the corresponding diagrams for $T^2 \times S^2$ and $T^2 \tilde{\times} S^2$ using our gluing technique. Furthermore, we provide an alternate proof of the fundamental result of Gay and Kirby which says that every closed $4$-manifold admits a trisection. The key feature of our proof is that Cerf theory takes a back seat to contact geometry.

The first author was supported by the UC Davis Chancellor’s Postdoctoral Fellowship Program. The second author was partially supported by a BIDEP-2219 research grant of the Scientific and Technological Research Council of Turkey.

Received 1 August 2017

Accepted 22 April 2018

Published 12 August 2019