“…Picone [17] (see also Allegretto [18]) generalized (1.2) to a Laplacian that, for differentiable functions and , Allegretto and Huang [19], Dunninger [20] independently extended (1.3) to a p -Laplacian, for differentiable functions and , and applied (1.4) to derive a Sturmian comparison principle, Liouville’s theorem, the Hardy inequality, and some profound results for p -Laplace equations and systems. For other generalizations of the Picone identities and applications, see Bal [21], Dwivedi [22], Dwivedi and Tyagi [23], Niu, Zhang and Wang [24], Tyagi [25]. These results indicate that Picone identities are seemingly simple in form, but extremely useful in the study of partial differential equations, and they have become an important tool in the analysis.…”