Equation Icon  g = η + f k k , η = diag(− 1, 1,1,1) μν μν μ ν μν -2M--r3-- f = r4 + a2z2 , k = 1, t rx + ay kx = -------, r2 + a2 k = ry-−-ax, y r2 + a2 z- kz = r, (9 )