The Inverse Problem of the Calculus of Variations for Scala Fourth Order Ordinary Differential Equations
Trans. Amer. Math Soc.
The Inverse Problem of the Calculus of Variations for Scalar Fourth Order Ordinary Deferential Equations, M.E. Fels, Trans. Amer. Math Soc., 348(12), 1996, 5007-5029.
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