theorem
  a<>0 & delta(a,b,c)>=0 & Polynom(a,b,c,0,z)=0 implies z = (-b+sqrt
delta(a,b,c))/(2*a) or z = (-b-sqrt delta(a,b,c))/(2*a) or z = -b/(2*a) or z =
  0
proof
  assume that
A1: a<>0 & delta(a,b,c)>=0 and
A2: Polynom(a,b,c,0,z)=0;
  (a*z^2+b*z+c)*z = 0 by A2;
  then Polynom(a,b,c,z) = 0 or z = 0;
  hence thesis by A1,Th1;
end;
