Softly higher-derivative massive gravity C. A. S. Almeida, W. T. Cruz, R. V. Maluf, A. Yu. Petrov and P. Porfirio Eur. Phys. J. C, 82 8 (2022) 715 Published online: 17 August 2022 DOI: 10.1140/epjc/s10052-022-10681-7