First integrals of ordinary linear differential systems
  The spectral method for building first integrals of ordinary linear differential systems is elaborated. Using this method, we obtain bases of first integrals for linear differential systems with constant coefficients, for linear nonautonomous differential systems integrable in closed form (algebraic reducible systems, triangular systems, the Lappo-Danilevskii systems), and for reducible ordinary differential systems with respect to various transformation groups. 
V. N. Gorbuzov, A. F. Pranevich
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