Homogeneous cosmologies in generalized modified gravity
  Dynamical system methods are used in the study of the stability of spatially flat homogeneous cosmologies within a large class of generalized modified gravity models in the presence of a relativistic matter-radiation fluid. The present approach can be considered as the generalization of previous works in which only $F(R)$ cases were considered. Models described by an arbitrary function of all possible geometric invariants are investigated and general equations giving all critical points are derived. 
Guido Cognola, Sergio Zerbini