“…In the case of dRGT massive gravity, f µν is not a dynamical but a fixed metric, and hence we need not consider the equations of motion for f µν . The class of solutions with C(t, r) = 0 includes the cosmological solutions [26,27], the black hole solutions [76][77][78][79], the Lemaître-Tolman-Bondi (LTB) solution [27], and the Reissner-Nordström (RN) solution [77]. Since the equations of motion for g µν (and, in fact, those for f µν as well) reduce to the Einstein equations with a cosmological constant, any spherically symmetric solution in GR is also a solution of the one-parameter subclass (3.11) of bi-gravity and massive gravity with a suitable fiducial metric.…”