Rotational symmetry of ancient solutions to the Ricci flow in dimension $3$ -- The compact case

Abstract: In [4], we proved that every noncompact ancient $\kappa$-solution to the Ricci flow in dimension $3$ is either locally isometric to a family of shrinking cylinders, or isometric to the Bryant soliton. In the same paper, we announced that the same method implies that compact ancient $\kappa$-solutions are rotationally symmetric. In this note we provide the details of this argument.