theorem
  for a, b, x being Complex holds a <> 0 & Polynom(a,b,x) = 0
  implies x = -(b/a)
proof
  let a, b, x be Complex;
  assume that
A1: a <> 0 and
A2: Polynom(a,b,x) = 0;
  a"*(-b) = a"*(a*x) by A2
    .= (a"*a)*x;
  then 1*x = a"*(-b) by A1,XCMPLX_0:def 7;
  then x = -(a"*b);
  hence thesis by XCMPLX_0:def 9;
end;
