Dana S. Richards, Jeffrey S. Salowe. A simple proof of Hwang's theorem for rectilinear Steiner minimal trees. Annals OR, 33(7):549-556, 1991. [doi]
@article{RichardsS91,
title = {A simple proof of Hwang's theorem for rectilinear Steiner minimal trees},
author = {Dana S. Richards and Jeffrey S. Salowe},
year = {1991},
doi = {10.1007/BF02067241},
url = {https://doi.org/10.1007/BF02067241},
researchr = {https://researchr.org/publication/RichardsS91},
cites = {0},
citedby = {0},
journal = {Annals OR},
volume = {33},
number = {7},
pages = {549-556},
}