Fully non-linear elliptic equations on compact Hermitian manifolds

We derive a priori estimates for solutions of a general class of fully non-linear equations on compact Hermitian manifolds. Our method is based on ideas that have been used for different specific equations, such as the complex Monge-Amp`ere, Hessian and inverse Hessian equations. As an application we solve a class of Hessian quotient equations on K"ahler manifolds assuming the existence of a suitable subsolution. The method also applies to analogous equations on compact Riemannian manifolds.