On the symmetry properties of the PT kernels and recurrence relations
  Perturbation Theory to Large Scale Structure Cosmology proposes corrections
to the linearly evolved density contrast and velocity in terms of a series
development in which all terms are integrals of powers of the linear density
contrast multiplied by kernels. We discuss the symmetry properties of these
kernels and show that their full symmetrized versions can be decomposed in
different classes of subkernels. We will construct classes of subkernels with
improved symmetry properties, and provide recurrence relations to generate
them.
