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;
