The Onsager Symmetry Relation and the Time Inversion Invariance of the   Entropy Production
  Starting from the entropy production being invariant under time reversal, one can (i) easily proof, and understand, many aspects of the linear Onsager relations and (ii) deduce the result that all quadratic Onsager coefficients for hydrodynamic fluxes vanish. 
Mario Liu (Institut f\"ur Theoretische Physik, Universit\"at Hannover,   Hannover, Germany, EC)