p2 := (x+f0)**2+f1;
p4 := (p2+f2)*(p2+x)+f3;
p4x := x**4-3*x**3+x**2-101*x+3;
eq := expand(p4x-p4);
for i from 0 to 4 do eq.i := coeff(eq,x,i) od;
