Vukmirović, S., and T. Šukilović. “Geodesic Completeness of the Left-Invariant Metrics on ${{\mathbb{R}} H^n} $”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 72, no. 5, Mar. 2020, pp. 611–619, doi:10.37863/umzh.v72i5.645.