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2. W. Hurewitz, Lectures on Ordinary Differential Equations (The M.I.T. Press, London, 1970).
3. E. A. Coddington and N. Levinson, Theory of Ordinary Differential Equations (McGraw-Hill, Inc., USA, 1955).
4. V. P. Gupta and P. K. Jain, Lebesgue Measure and Integration (Wiley, New York, 1986).
5. R. G. Bartle, A Modern Theory of Integration (American Mathematical Society, USA, 2000).