reserve a,b,c for positive Real,
  m,x,y,z for Real,
  n for Nat,
  s,s1,s2,s3,s4,s5 for Real_Sequence;

theorem Th9:
  (x+y)^2>=4*x*y
proof
  2*((x^2+y^2)/2)>=2*(x*y) by Th7,XREAL_1:64;
  then x^2+y^2+2*x*y>=2*x*y+2*x*y by XREAL_1:6;
  hence thesis;
end;
