HILDEBRANDT, Stefan; KAUL, Helmut; WIDMAN, Kjell-ove. Harmonic mappings into Riemannian manifolds with non-positive sectional curvature. Mathematica Scandinavica, Berkeley, CA, United States, v. 37, p. 257–263, 1975. DOI: 10.7146/math.scand.a-11604. Disponível em: https://journals.msp.org/mscand/article/view/2069. Acesso em: 25 jul. 2026.