  In the semiclassical treatment of gravity, an external observer can measure
only the mean (not the exact) mass of the black hole (BH). By contrast, in
fully quantum gravity the exact (not only mean) BH mass is measurable by the
external observer. This additional information (missing in the semiclassical
treatment) available to the external observer significantly helps to understand
how information leaks out during the BH evaporation.
