“…More recently, Krause and Michel [16] proved the converse of this result in the case of linear equations and showed that in fact a linear scalar equation is of maximal symmetry if and only if it is iterative. Some recent results have also been obtained about linear scalar equations of maximal symmetry, concerning their transformation properties [17,18], their coefficient characterization [19,20,17], their first integrals or Hamiltonian forms [21,22].…”