Pop, P. C., A. Horvat-Marc, and C. Pop Sitar. “An Approximation Algorithm for the at Least Version of the Generalized Minimum Spanning Tree Problem”. Rev. Anal. Numér. Théor. Approx., vol. 35, no. 1, Feb. 2006, pp. 95-103, doi:10.33993/jnaat351-1016.