Moerkotte, G., Fender, P., & Eich, M. (2013). On the correct and complete enumeration of the core search space. SIGMOD, 493. https://doi.org/10.1145/2463676.2465314

This paper presents the TBA (transformation-based approach) to solve the join reordering problem. It purposes 3 conflict detectors. All of them are correct, but only the last one is complete. Also, all of them do not require join predicates to be null intolerant.