Conformal entropy and stationary Killing horizons

Using Virasoro algebra approach, black hole entropy formula for a general class of higher curvature Lagrangians with arbitrary dependence on Riemann tensor can be obtained from properties of stationary Killing horizons. The properties used are a consequence of regularity of invariants of Riemann tensor on the horizon. As suggested by an example Lagrangian, eventual generalisation of these results to Lagrangians with derivatives of Riemann tensor, would require assuming regularity of invariants involving derivatives of Riemann tensor and that would lead to additional restrictions on metric functions near horizon.