Perturbative Symmetry Approach
  Perturbative Symmetry Approach is formulated in symbolic representation. Easily verifiable integrability conditions of a given equation are constructed in the frame of the approach. Generalisation for the case of non-local and non-evolution equations is disscused. Application of the theory to the Benjamin-Ono and Camassa-Holm type equations is considered. 
A.V. Mikhailov, V.S. Novikov