Li, J., D. Harabor, P. J. Stuckey, H. Ma, and S. Koenig. “Symmetry-Breaking Constraints for Grid-Based Multi-Agent Path Finding”. Proceedings of the AAAI Conference on Artificial Intelligence, vol. 33, no. 01, July 2019, pp. 6087-95, doi:10.1609/aaai.v33i01.33016087.