“…Within the gauge/gravity correspondence, the subsystem complexity has been evaluated both in static [12,16,75,[83][84][85][86] and in time dependent gravitational backgrounds [87][88][89][90]. In static backgrounds, it is given by the volume identified by the minimal area hypersurface anchored to the boundary of the subsystem, whose area provides the holographic entanglement entropy [91] (for static black holes, this hypersurface does not cross the horizon [92][93][94]), while, in time dependent gravitational spacetimes, the extremal hypersurface occurring in the covariant proposal for the holographic entanglement entropy [66] must be employed.…”