M. Rimoldi, G. Veronelli: $f$-Harmonic maps and applications to gradient Ricci solitons (Submitted Paper) 2011 G. Catino, C. Mantegazza, L. Mazzieri, M. Rimoldi: Locally Conformally Flat Quasi-Einstein Manifolds J. Reine Angew. Math. (Crelle's Journal) Vol. 675 (2013), p. 181-189, 2013 C. Mantegazza, S. Mongodi, M. Rimoldi: The Cotton Tensor and the Ricci Flow Geometric Flows Vol. 2, p. 49-71, 2017 S. Honda, L. Mari, M. Rimoldi, G. Veronelli: Density and non-density of $C^\infty_c \hookrightarrow W^{k,p}$ on complete manifolds with curvature bounds Nonlinear Anal. (preprint) Vol. 211, p. 26, 2021