Originating from research in the qualitative theory of ordinary differential equations this
book follows the authors' work on structurally stable planar quadratic polynomial differential
systems. In the present work the authors aim at finding all possible phase portraits in the
Poincaré disc modulo limit cycles of planar quadratic polynomial differential systems
manifesting the simplest level of structural instability. They prove that there are at most 211
and at least 204 of them.
