Compare a tuple : I want to compare 2 tuple `T1` and `T2`, which are both three-element-tuple, by firstly comparing `T[0]`, if `T1[0]==T2[0]`, then compare `T1[1]` and `T2[1]`, if `T1[1]==T2[1]` then compare `T1[2]` and T2[2].
