Krzysztof R. Apt, Peter van Emde Boas, Angelo Welling. The STO-Problem is NP-Hard. Journal of Symbolic Computation, 18(5):489-495, 1994.
@article{AptBW94,
title = {The STO-Problem is NP-Hard},
author = {Krzysztof R. Apt and Peter van Emde Boas and Angelo Welling},
year = {1994},
researchr = {https://researchr.org/publication/AptBW94},
cites = {0},
citedby = {0},
journal = {Journal of Symbolic Computation},
volume = {18},
number = {5},
pages = {489-495},
}