A Theorem of Bochner, Revisited

Many hierarchies of the theory of solitons possess symmetries which do not belong to the hierarchy itself. These symmetries are known under the various names of additional, master or conformal symmetries. They were discovered by Fokas, Fuchssteiner and Oevel [9], [10], [25], Chen, Lee and Lin [4] and Orlov and Schulman [26]. They are intimately related to the bihamiltonian nature of the equations of the theory of solitons which was pioneered in the work of Magri [23] and Gel’fand and Dorfman [11].

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