Birkhoff’s theorem in f(R) theory of gravity P. J. Ravindranath, Y. Aditya, D. R. K. Reddy and M. V. Subba Rao Eur. Phys. J. Plus, 133 9 (2018) 376 Published online: 20 September 2018 DOI: 10.1140/epjp/i2018-12241-5