Instability of the Kerr Cauchy horizon

Consider generic initial data giving rise to a perturbation of a Kerr black hole governed by the Einstein vacuum equations, and let the perturbed spacetime have a Cauchy horizon. Instability of the Kerr Cauchy horizon. For generic initial data, perturbations of Kerr black holes governed by the Einstein vacuum equations are inextendible across the (perturbed) Cauchy horizon in a suitable regularity class. This is the nonlinear counterpart of the blueshift instability observed for scalar waves on Kerr backgrounds: although the metric may remain bounded up to the Cauchy horizon, transverse derivatives can blow up. The paper proves instability in the Lipschitz regularity class under a precise nonlinear Price's-law-type estimate, while the broader generic statement remains open.