theorem
  b<>0 & delta(b,c,d)>=0 & Polynom(0,b,c,d,z)=0 implies z = (-c+sqrt
  delta(b,c,d))/(2*b) or z = (-c-sqrt delta(b,c,d))/(2*b) or z = -c/(2*b)
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,Th1;
end;
