Givental construction of nonorientable Lagrangian surfaces
= Givental construction of nonorientable Lagrangian surfaces
{c}
For every $l\geq1$, take a plane immersed circle with $l$ transverse double points and form its product with an embedded circle in a second symplectic plane. The resulting torus is a <Product Lagrangian immersion> with $l$ clean double circles. Resolving them gives a connected nonorientable <Lagrangian embedding> in $\mathbb R^4$ with Euler characteristic $-4l$.