This review paper contains a brief summary of topics and concepts related with some open
problems of planar differential systems. Most of them are related with 16th Hilbert problem …

Св и з зйжк н л к в гк жк л г и ж зйаиз г и в в и зий н г зг жгвгйз ви жз г к игж Ќ а з в и да в К
Ь з д д ж гвз зиз г илг д жизК Св и Ќжзи гв Дз и гвз Оп ЕИ л ж к л згб в ж а и в ей з и и джгк …

We study the period functionTof a centerOof a Liénard system. A sufficient condition for the
monotonicity ofT, or for the isochronicity ofO, is given. Such a condition is also necessary …

The computation of period constants is a way to study isochronous center for polynomial
differential systems. In this article, a new method to compute period constants is given. The …

In this work we study isochronous centers of two-dimensional autonomous system in the
plane with linear part of center type and non-linear part given by homogeneous polynomials …

In this work we study isochronous centers of two-dimensional autonomous system in the
plane with linear part of center type and nonlinear part given by homogeneous polynomials …

In this paper, we study the codimension four quadratic system Q4: ż=− iz+ 4z2+ 2∣ z∣
2+(b+ ic) z̄2, where b and c are real constants, i2=− 1, z= x+ iy,∣ b+ ic∣= 2. It is proved …

The paper deals with polynomials systems with degenerate infinity from different points of
view. We show the utility of the projective techniques for such systems, and a more detailed …

In this paper, we investigate the linearizability problem for the two-dimensional planar
complex system. The necessary and sufficient conditions for the linearizability of this system …

This article contains a brief summary of the topics and concepts related to 16b Hilbert
problem which refers to the existence of a bound on the number of limit cycles of a …