“…In fact, Yau proposed a more general version of this problem that is involved with the σ k , k = 1, 2, • • • , n of Ricci tensor in [40]. Unfortunately, Yang [38] constructs a counterexample on Kähler manifold to prove that the general version of Yau's Problem 1.5 does not hold for k = 1, 2, • • • , n − 1, Xu [37] obtains an estimate involved with the integral of scalar curvature towards the Problem 1.5 in the case of three-dimensional Riemannian manifold by using the monotonicity formulas of Colding and Minicozzi [5]. However, Problem 1.5 remains open.…”