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 $C(0,1)$.
Show that the unique element of the set $\mathcal{D}_{P_C}$ is the restriction to $\bar{D}(0,1)$ of a polynomial of degree less than or equal to $m$.