theorem
  b<>0 & delta(b,c,d)<0 & Polynom(0,b,c,d,z)=0 implies z = -c/(2*b)+(
sqrt (-delta(b,c,d))/(2*b))*<i> or z = -c/(2*b)+(-sqrt (-delta(b,c,d))/(2*b))*
  <i>
proof
  assume that
A1: b<>0 & delta(b,c,d)<0 and
A2: Polynom(0,b,c,d,z)=0;
  Polynom(b,c,d,z)=0 by A2;
  hence thesis by A1,Th2;
end;
