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I wonder what is the nature of a black hole as set of points of manifold. A single point (with infinite curvature) or a "trench" ? I thought that it is a "point", but since black holes can collide and merge there, should be, I believe, some "before" with two singularities and some "after" with only one. Black hole as whole should have some world-line which ends up in the big crunch (if it happens).