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2. Earl A. Coddington. “An Introduction to Ordinary Differential Equations” Dover Publications, Print ISBN: 9780486659428, 0486659429, eText ISBN: 9780486131832, 0486131831, New York, Vol 6, No 11(1989), pp 33-43, Pages: 320.
3. Hybrid Legendre Block-Pulse functions method for solving partial differential equations with non-local integral boundary conditions