  In Class. Quantum Grav. 35 (2018) 155015 we have introduced the notion of
"Multiple Killing Horizon" and analyzed some of its general properties.
Multiple Killing Horizons are Killing horizons for two or more linearly
independent Killing vectors simultaneously. In this paper we focus on the
vacuum case, possibly with cosmological constant, and study the emergence of
Multiple Killing Horizons in terms of characteristic initial value problems for
two transversally intersecting null hypersurfaces. As a relevant outcome, a
more general definition of Near Horizon Geometry is put forward. This new
definition avoids the use of Gaussian null coordinates associated to the
corresponding degenerate Killing vector and thereby allows for inclusion of its
fixed points.
