On a general vacuum solution of fourth-order gravity

The authors generalise the result derived for the Einstein theory with the cosmological term (the general asymptotic solution containing four arbitrary functions of three coordinates) to fourth-order gravity. For scale-invariant fourth-order gravity the expanding generalised de Sitter solution is found to be an attractor, i.e. for t to infinity an open neighbourhood of solutions approach this one. For (R+R² gravity), one obtains an intermediate de Sitter stage with a high probability that is followed by a power-law Friedman stage. Finally, they argue that the inclusion of ordinary inhomogeneously distributed matter does not alter these results.