theorem
  2/((1/a)+(1/b))<=sqrt((a^2+b^2)/2)
proof
A1: 2/((1/a)+(1/b))<=(a+b)/2 by Th10;
  (a+b)/2<=sqrt((a^2+b^2)/2) by Th8;
  hence thesis by A1,XXREAL_0:2;
end;
