Nonlinear variable exponent Picone identity and $p(x)$-sub-Laplacian first eigenvalue for general vector fields

In this paper, we establish a new generalized nonlinear variable exponent Picone identities for $p(x)$-sub-Laplacian. As applications we prove uniqueness, simplicity, momotonicity and isolatedness of the first nontrivial Dirichlet eigenvalue of $p(x)$-sub-Laplacian with respect to the general vector fields. Further applications yield Hardy type inequalities and Caccioppolli estimates with variable exponents.