-model structure is responsible for various distinguished features of the stationary Einstein–Maxwell
(EM) system and related self-gravitating matter models. This section is devoted to a brief discussion of
some applications: We argue that the Mazur identity [133
], the quadratic mass formulas [89] and the
Israel–Wilson class of stationary black holes [102, 145] owe their existence to the 
-model structure of
the stationary field equations.
