“…x is the Hessian matrix of f , κ > 0 is a constant. Then (Q, T)-rotating-periodic system (23)-(24) has at least one (Q, T)-rotating-periodic solution.Proof Let φ(t) = C for some C > 0. For any t ∈ [0, T], |x| = C, we havex, f (t, x) = x, f (t, 0) + f x t, ξ (t) x ≤ x, f (t, 0) -κ|x| 2 ≤ 0 for C ≥ M 0 /κ, where M 0 = max t∈[0,T] |f (t, 0)|.…”