The spread construction and non-uniqueness of visible Lagrangians

Every even symplectic Hirzebruch surface contains a Lagrangian torus and every odd symplectic Hirzebruch surface contains a Lagrangian Klein bottle as their respective real locus.

From a toric point of view, this is a visible Lagrangian which surjects to the full moment polytope under the moment map.

In this paper, we prove that every Hirzebruch surface contains both a Lagrangian torus and a Lagrangian Klein bottle with this property.

An interesting consequence is that the topology of visible Lagrangian submanifolds is not determined by their image under the moment map.

The proof is based on a new construction, which we call the spread of a family of Hamiltonian diffeomorphisms.