Abstract. Odani has shown that if deg g ≤ deg f then after deleting some trivial cases the polynomial systemẋ = y,ẏ = −f (x)y − g(x) does not have any algebraic invariant curve. Here we almost completely solve the problem of algebraic invariant curves and algebraic limit cycles of this system for all values of deg f and deg g. We give also a simple presentation of Yablonsky's example of a quartic limit cycle in a quadratic system.
The resultsThe subject of this work is the polynomial Liénard systeṁwhereare polynomials of degrees m and n respectively (a m b n = 0). Odani in [3] investigated algebraic phase curves of (1). He proved that if n ≤ m andthen the vector field (1) does not have any algebraic invariant curve.He also presented the example of Wilson [6] withand the algebraic limit cycleOdani conjectured that if m < n < 2m + 1 then (1) does not have algebraic limit cycles. Here we show that this conjecture is false, and we solve the problem of algebraic limit cycles and algebraic invariant curves for all pairs (m, n) almost completely.In what follows we consider systems of the form (1) with the restriction (2) and denote by A m,n the space of such systems,