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We consider the Dirichlet problem \begin{equation*} - \Delta^{K_p}_{p(x)} u(x) - \Delta^{K_q}_{q(x)} u(x) = f(x,u(x), \nabla u(x)) \quad \mbox{in }\Omega, \quad u\big{|}_{\partial \Omega}=0, \end{equation*} driven by the sum of a $p(x)$-Laplacian operator and of a $q(x)$-Laplacian operator, both of them weighted by indefinite (sign-changing) Kirchhoff type terms. We establish the existence of weak solution and strong generalized solution, using topological tools (properties of Galerkin basis and of Nemitsky map). In the particular case of a positive Kirchhoff term, we obtain the existence of weak solution ($=$ strong generalized solution), using the properties of pseudomonotone operators.

We consider a nonlinear elliptic problem driven by the Dirichlet $p$-Laplacian and a reaction term which depends also on the gradient (convection). No growth condition is imposed on the reaction term $f(z, \cdot,y)$. Using topological tools and the asymptotic analysis of a family of perturbed problems, we prove the existence of a positive smooth solution.

We prove the existence of weak solutions to the Dirichlet boundary value problem for equations involving the $p(x)$-Laplacian-like operator in the principal part, with reaction term satisfying a sub-critical growth condition. We establish the existence of at least one nontrivial weak solution and three weak solutions, by using variational methods and critical point theory.