1. Borghini, S., Mazzieri, L.: Counterexamples to a divergence lower bound for the covariant derivative of skew-symmetric $$2$$-tensor fields, Preprint
2. Catino, G., Dameno, D., Mastrolia, P.: Private Communication
3. Yun, G., Hwang, S.: Besse conjecture with positive isotropic curvature. Ann. Global Anal. Geom. 62, 507–532 (2022)