You Cannot Press Out the Black Hole
  It is shown that a ball-shaped black hole region homeomorphic with D**n cannot be pressed out, along whichever axis penetrating the black hole region, into a black ring with a doughnut-shaped black hole region homeomorphic with S**1 x D**(n-1). A more general prohibition law for the change of the topology of black holes, including a version of no-bifurcation theorems for black holes, is given. 
Daisuke Ida and Takahiro Okamoto
gr-qc hep-th math-ph math.MP