1. “Lectures on Differential Equations”;Petrovsky,1952
2. “Differential Equations.”;Stepanov,1950
3. “Qualitative Theory of Differential Equations”;Nemyckii,1949
4. “The Theory of Ordinary Differential Equations.”;Coddington,1955
5. “Differential Equations: Geometric Theory.”;Lefschetz,1957