Let the function f be absolutely continuous on [a, b]. Prove: (i) If f is Liptschitz on [a, b], then there is a constant M> 0 such that f'| M a.e. on [a, b]. (ii) If there is a constant M >0 such that f'M a.e. on [a, b], then f is Liptschitz on [a, b].