  Black holes evolve by evaporation of their event horizon. While this process
is believed to be unitary, there is no consensus on the recovery of information
in black hole entropy. A missing link is a unit of information in black hole
evaporation. Distinct from Hawking radiation, we identify evaporation in
entangled pairs by $\mathbb{P}^2$ topology of the event horizon consistent with
the Bekenstein-Hawking entropy in a uniformly spaced horizon area, where $k_B$
denotes the Boltzmann constant. It derives by continuation of $\mathbb{P}^2$ in
Rindler spacetime prior to gravitational collapse, subject to a tight
correlation of the fundamental frequency of Quasi-Normal-Mode (QNM) ringing in
gravitational and electromagnetic radiation. Information extraction from
entangled pairs by detecting one over the surface spanned by three faces of a
large cube carries a unit of information of $2\log3$ upon including measurement
of spin.
