Matthias Beck. Problem 10918. The American Mathematical Monthly, 109(1):77, 2002. [doi]
@article{Beck02-0, title = {Problem 10918}, author = {Matthias Beck}, year = {2002}, url = {http://www.jstor.org/stable/2695776}, researchr = {https://researchr.org/publication/Beck02-0}, cites = {0}, citedby = {0}, journal = {The American Mathematical Monthly}, volume = {109}, number = {1}, pages = {77}, }