All second order scalar differential invariants of symplectic hyperbolic and elliptic Monge-Ampère equations with respect to symplectomorphisms are explicitly computed. In particular, it is shown that the number of independent second order invariants is equal to 7, in sharp contrast with general Monge-Ampère equations for which this number is equal to 2. We also introduce a series of invariant differential forms and vector fields which allow us to construct numerous scalar differential invariants...

The notes consist of a study of special Lagrangian linear subspaces. We will give a condition for the graph of a linear symplectomorphism $f:({ℝ}^{2n},\sigma ={\sum }_{i=1}^{n}d{x}_i\wedge d{y}_i)\to ({ℝ}^{2n},\sigma )$ to be a special Lagrangian linear subspace in $({ℝ}^{2n}\times {ℝ}^{2n},\omega =\pi *₂\sigma -\pi *₁\sigma )$. This way a special symplectic subset in the symplectic group is introduced. A stratification of special Lagrangian Grassmannian $S{\Lambda }_{2n}\simeq SU\left(2n\right)/SO\left(2n\right)$ is defined.

We construct a family of Lagrangian submanifolds in the complex sphere which are foliated by $(n-1)$-dimensional spheres. Among them we find those which are special Lagrangian with respect to the Calabi-Yau structure induced by the Stenzel metric.

We give a canonical construction of an “isotropic average” of given $C^1$-close isotropic submanifolds of a symplectic manifold. For this purpose we use an improvement (obtained in collaboration with H. Karcher) of Weinstein’s submanifold averaging theorem and apply “Moser’s trick”. We also present an application to Hamiltonian group actions.

In [Ch00], Chekanov showed that the Hofer norm on the Hamiltonian diffeomorphism group of a geometrically bounded symplectic manifold induces a nondegenerate metric on the orbit of any compact Lagrangian submanifold under the group. In this paper we consider the orbits of more general submanifolds. We show that, for the Chekanov–Hofer pseudometric on the orbit of a closed submanifold to be a genuine metric, it is necessary for the submanifold to be coisotropic, and we show that this condition is...