Optionall: number = 0the lower(or left) bound of interval
Optionalr: number = 0the upper(or right) bound of interval
the lower(or left) bound of interval
the upper(or right) bound of interval
clone this interval
if a number in this interval
the number
if the interval equals to the other interval
the other interval
the length of interval
the other interval merge other interval to this interval
if the interval onverlaps the other interval
the other interval
interval of number