Finite-time future singularities in modified Gauss–Bonnet and ℱ(R,G) gravity and singularity avoidanceKazuharu Bamba, Sergei D. Odintsov, Lorenzo Sebastiani and Sergio ZerbiniEur. Phys. J. C, 67 1-2 (2010) 295-310DOI: https://doi.org/10.1140/epjc/s10052-010-1292-8