Transformations for the Camassa-Holm Equation, Its High-Frequency Limit and the Sinh-Gordon Equation.

In this article we present a new transformation between two integrable hierarchies of the Camassa-Holm equation and the Hunter-Saxton equation. For instance we present a transformation between the Harry-Dym equation and the extended Harry-Dym equation. Moreover, we describe a relationship between the Hunter-Saxton equation, which is the high-frequency limit of the Camassa-Holm equation, and the Sinh-Gordon equation by a reciprocal transformation.