A new kind of deformation related to the Korteweg–de Vries hierarchy and its master symmetries is studied. The algebra of deformations is generated by trivial (point) transformations via a special recursion operator and proved to preserve Huygens’ principle for a certain family of hyperbolic linear equations. The corresponding evolution flows for Hadamard coefficients are presented explicitly. The connections with spectral deformations and Darboux transformations as well as recent works on the bispectral problem for a Schrödinger operator are discussed.

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