“…In this case an essentially closed-form solution, requiring a determination of the positive real root of a real cubic equation by Cardano's method, is possible (including a complete enumeration of special cases). Although no closedform solution for the roots of higher-order polynomials is possible, there has been considerable progress in elucidating their fundamental nature, and in developing numerical methods to compute them [1,2,9,10,11,14,16,19,20,21,22,23]. In particular, it has been shown that the set of roots of any polynomial f (X ) ∈ H[X ] is a finite union of singletons and 2-spheres.…”