  Let $M$ be a manifold and $\Lambda$ a compact exact connected Lagrangian
submanifold of $T^*M$. We can associate with $\Lambda$ a conic Lagrangian
submanifold $\Lambda'$ of $T^*(M\times R)$. We prove that there exists a
canonical sheaf $F$ on $M\times R$ whose microsupport is $\Lambda'$ outside the
zero section. We deduce the already known results that the Maslov class of
$\Lambda$ is $0$ and that the projection from $\Lambda$ to $M$ induces
isomorphisms between the homotopy groups.
