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2. Notes on a differential equation which occurs in the two-dimensional motion of a compressible fluid, and the associated variational principle;Bateman,1929
3. On Hamilton's principle for perfect compressible fluids;Taub,1949
4. The variational method in hydrodynamics;Lush;Quart. Mech. Appl. Math.,1956
5. Variational methods and applications to water waves;Whitham,1967