A Darboux theorem for Hamiltonian operators in the formal calculus of   variations
  We prove a Darboux theorem for formal deformations of Hamiltonian operators of hydrodynamic type (Dubrovin-Novikov). Not all deformations are equivalent to the original operator: there is a moduli 2-stack of normal forms.   The paper utilizes three main concepts:   1) dg Lie algebras concentrated in degrees [-1,\infty) such as the Schouten algebra - these give a convenient language for describing deformation problems;   2) the Deligne 2-groupoid associated to such a dg Lie algebra, which represents the moduli of formal deformations;   3) a refined version of the Schouten bracket in the formal calculus of variations, due to V. O. Soloviev (hep-th/9305133). 
Ezra Getzler (RIMS and Northwestern)