1. George Pólya and Gordon Latta, Complex Variables. Wiley. 1974.
2. Jerrold E. Marsden, Basic Complex Analysis. Freeman. 1973.
3. V. I. Arnold, Ordinary Differential Equations, MIT. 1973.
4. Peter Henrici, Essentials of Numerical Analysis, Wiley, 1982. section 2.5.