We study the local classification of higher order Fuchsian linear differential equations under various refinements of the classical notion of the "type of differential equation" introduced by Frobenius. The main source of difficulties is the fact that there is no natural group action generating this classification. We establish a number of results on higher order equations which are similar but not completely parallel to the known results on local (holomorphic and meromorphic) gauge equivalence of systems of first order equations.Keywords Fuchsian singularity · Gauge classification · Resonance · Weyl algebra 1 Local Classification of Linear Ordinary Differential Equations
Systems and Higher Order EquationsThe local analytic theory of linear ordinary differential equations exists in two parallel flavours, either that of systems of several first order equations, or of scalar (higher order) equations. One can relatively easily transform one type of objects to the other, yet this transformation loses some additional structures.Let k be a differential field, called the field of coefficients. We will be interested almost exclusively in the field M = M (C 1 , 0) of meromorphic germs at the origin t = 0 on the complex line C = C 1 , the quotient field of the ring O = O(C 1 , 0) of