Let $m$ be an integer greater than or equal to 2. We consider a polynomial $P \in \mathcal{P}_m$ and we denote by $P_C$ the restriction of $P$ to the circle $C(0,1)$.
Explicitly determine the set $\mathcal{D}_{P_C}$ when the polynomial $P$ is defined by $P(x,y) = x^3$.