Liouville class of a Lagrangian submanifold
= Liouville class of a Lagrangian submanifold
{c}
{title2=$[\lambda|_L]$}
For a Lagrangian submanifold $L\subset(\mathbb R^{2n},d\lambda)$, the restriction $\lambda|_L$ is closed. Its cohomology class is preserved by ambient symplectomorphisms because every closed one-form on $\mathbb R^{2n}$ is exact. On a product torus of circles, its periods are the enclosed symplectic areas of the factors.