On the Global Center of Polynomial Differential Systems of Degree 2k + 1

If P(x,y) and Q(x,y) are analytic functions, then systems (A) d x d t = P ( x , y ) , d y d t = Q ( x , y ) , https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003067498/6ba0c26b-f086-40cc-86ed-1693dc596221/content/eq7017.tif"/>