This is why, although the “simple” α = 1 function is known to represent very well the gravitational field of spiral galaxies [141Jump To The Next Citation Point, 166Jump To The Next Citation Point, 402Jump To The Next Citation Point, 508Jump To The Next Citation Point], we use, in Section 6.5.1, the γ = δ = 1 function of Eq. 52View Equation and Eq. 53View Equation in order to fit spiral galaxy rotation curves.