About lagrangian fibrations on symplectic fourfolds

It is known that for any lagrangian fibration $M \to X$, one can prove that $X$ is always a projective space if $X$ is smooth or for some special cases of manifold $M$. In this talk i will explain the work of Ou. He has proved that for a lagrangian fibration $M \to X$ from irreducible symplectic fourfold $M$ the base $X$ is either projective plane or Fano surface $S^n(E_8)$.