*(English)*Zbl 1009.34033

This is a very nice paper about oscillatory properties of the second-order dynamic equation

on an arbitrary time scale $\mathbb{T}$. Equation (1) contains as special cases the well known second-order Sturm-Liouville differential $(\mathbb{T}=\mathbb{R})$ and difference $(\mathbb{T}=\mathbb{Z})$ equations. A necessary and sufficient condition for the oscillation of equation (1) is established by transforming equation (1) into a scalar trigonometric system (other terminology is a self-reciprocal system). The classification of (1) to be oscillatory/nonoscillatory makes sense, since the time scales Sturmian separation theorem holds for equation (1). The main tool for the proof is the time scales trigonometric transformation. This transformation preserves the oscillatory behavior of transformed systems and generalizes the corresponding continuous-time $(\mathbb{T}=\mathbb{R})$ and discrete-time $(\mathbb{T}=\mathbb{Z})$ trigonometric transformations (the latter one obtained by *M. Bohner* and the first author [J. Differ. equations 163, No. 1, 113-129 (2000; Zbl 0956.39011)]). A further oscillation criterion for equation (1) is obtained via the Riccati technique.

This paper will be useful for researchers interested in (non)oscillatory behavior of differential, difference, and/or dynamic equations.