Institute of Mathematics and Informatics Bulgarian Academy of Sciences
Serdica Mathematical Journal, Vol. 31, No 3, (2005), 201p-216p
We show that for n = 4 they are realizable either
by hyperbolic polynomials of degree 4 or by non-hyperbolic polynomials of
degree 6 whose fourth derivatives never vanish (these are a particular case
of the so-called hyperbolic polynomial-like functions of degree 4).