reserve a,b,c,d,a9,b9,c9,d9,y,x1,u,v for Real,
  s,t,h,z,z1,z2,z3,s1,s2,s3 for Complex;

theorem
  z1<>0 & Polynom(z1,z2,0,z)=0 implies z=-(z2/z1) or z=0
proof
  assume that
A1: z1<>0 and
A2: Polynom(z1,z2,0,z)=0;
  0 =(z1*z+z2)*z by A2;
  then Polynom(z1,z2,z) = 0 or z=0;
  hence thesis by A1,Th16;
end;
