  The Gromov-Eliashberg theorem says that the group of symplectomorphisms of a
symplectic manifold is C^0-closed in the group of diffeomorphisms. This can be
translated into a statement about the Lagrangian submanifolds which are graphs
of symplectomorphisms. It is also known that such Lagrangian submanifolds are
locally microsupports of sheaves. We explain how we can deduce the
Gromov-Eliashberg theorem from the involutivity theorem of Kashiwara and
Schapira which says that the microsupport of a sheaf is coisotropic.
