Nearby Lagrangians in the cotangent bundle of the Klein bottle

Abstract

We prove the nearby Lagrangian conjecture for the Klein bottle: every closed connected embedded exact Lagrangian submanifold of its cotangent bundle is Hamiltonian isotopic to the zero section by a compactly supported isotopy. The proof passes to the torus double cover and builds on the theorem of Dimitroglou Rizell, Goodman, and Ivrii for the two-dimensional torus. The main step is to construct an isotopy compatible with the covering involution. We achieve this using holomorphic sphere rulings in $S^2\times S^2$ adapted to the zero section, allowing the construction to descend to the Klein bottle.