“…The tori are governed by "Boyer's condition" of the analytic theory of equilibrium configurations of rotating perfect fluids [65]. The toroidal structures of orbiting barotropic perfect fluid are determined by an effective potential reflecting the spacetime geometry, and the centrifugal force component through the distribution of the specific angular momentum (r) of the orbiting fluid - [26,66,67,64,68,69,70,71,72,73,74,56,75]. The entropy is constant along the flow and, according to the von Zeipel condition, the surfaces of constant angular velocity Ω and of constant specific angular momentum coincide [76,77,78] (this implies in particular that the rotation law = (Ω) is independent of the equation of state [64,79]).…”