read NormalBasis;

f :=
(x^4-3*x+1)*y^5-(6*x-1)*(x^2-2)*y^4*x+(x^3+12*x^2-21*x-2)*y^3*x^2
-(3*x^2-2*x-11)*y^2*x^3+x^5-(4*x+1)*y*x^3;

n := degree(f,y);

alpha := RootOf(f,y):

V := Candidates(f,x,y);

beta := select(has,V,y)[1];
beta :=  subs(y=alpha, beta):
m_beta := evala(Norm(y - beta));