M. Heusler, ON THE UNIQUENESS OF THE REISSNER-NORDSTROM SOLUTION WITH ELECTRIC AND MAGNETIC CHARGE, Classical and quantum gravity, 11(3), 1994, pp. 120000049-120000053
We give a straightforward generalization of the uniqueness proof for s
tatic electrovac black holes including the case of non-vanishing magne
tic charge. This also establishes the non-existence of multiple black
hole solutions of the Einstein-Maxwell system with electric and magnet
ic fields in a static, asymptotically flat spacetime.