Group classification of systems of non-linear reaction-diffusion   equations with general diffusion matrix. III. Triangular diffusion matrix
  Group classification of systems of two coupled nonlinear reaction-diffusion equation with a general diffusion matrix started in papers math-ph/0411027,, math-ph/0411028 is completed in present paper where all non-equivalent equations with triangular diffusion matrix are classified.   In addition, symmetries of diffusion systems with nilpotent diffusion matrix and additional first order derivative terms are described. 
A. G. Nikitin