
theorem Th57:
  for I be Interval holds diameter I = OS_Meas.I
proof
    let I be Interval;
    I in the set of all I where I is Interval; then
    OS_Meas.I <= diameter I &
    diameter I <= OS_Meas.I by Th44,Lm22,MEASUR10:def 1;
    hence thesis by XXREAL_0:1;
end;
