We determine that the maximum crossing number of C3×C3 is 78, which closes the previously best known range of between 68 and 80. The proof uses several techniques which may be useful in determining the maximum crossing number of other graphs.
@article{arxiv.2005.06699,
title = {The maximum crossing number of $C_3 \times C_3$},
author = {Michael Haythorpe and Alex Newcombe},
journal= {arXiv preprint arXiv:2005.06699},
year = {2020}
}