Stephen C. Johnson, Ronald L. Graham. Problem #7. ACM Comm. Computer Algebra, 8(1):4, 1974. [doi]
@article{JohnsonG74,
title = {Problem #7},
author = {Stephen C. Johnson and Ronald L. Graham},
year = {1974},
doi = {10.1145/1086823.1086825},
url = {http://doi.acm.org/10.1145/1086823.1086825},
researchr = {https://researchr.org/publication/JohnsonG74},
cites = {0},
citedby = {0},
journal = {ACM Comm. Computer Algebra},
volume = {8},
number = {1},
pages = {4},
}