“…Recall that when dimension n ≥ 3, the existence of solutions of the σ k -Yamabe problem has been proved for k ≥ n/2, k = 2 or when (M, g) is locally conformally flat, the compactness of the set of solutions has been proved for k ≥ n/2 when the manifold is not conformally equivalent to the standard sphere − they were established in [11,22,27,31,45,54,65]. For more recent works on σ k -Yamabe type problems, see for example [1,3,4,7,8,9,19,20,21,23,30,32,33,38,39,40,41,42,55,56,60,66,67,68] and references therein. However, there are still many challenging open problems on general compact Riemannian manifolds -the compactness remains open for 2 ≤ k ≤ n/2 and the existence remains open for 2 < k < n/2.…”