Ernest J. Cockayne, P. H. Spencer. On the independent queens covering problem. Graphs and Combinatorics, 4(1):101-110, 1988. [doi]
@article{CockayneS88,
title = {On the independent queens covering problem},
author = {Ernest J. Cockayne and P. H. Spencer},
year = {1988},
doi = {10.1007/BF01864158},
url = {http://dx.doi.org/10.1007/BF01864158},
researchr = {https://researchr.org/publication/CockayneS88},
cites = {0},
citedby = {0},
journal = {Graphs and Combinatorics},
volume = {4},
number = {1},
pages = {101-110},
}