The resolution tree problem consists of deciding whether a given sequence-like resolution refutation admits a tree structure. This paper shows the NP-completeness of both the resolution tree problem and a natural generalization of the resolution tree problem that does not involve resolution. © 2009 Elsevier B.V. All rights reserved.
Hoffmann, J. (2009). Finding a tree structure in a resolution proof is NP-complete. Theoretical Computer Science, 410(21–23), 2295–2300. https://doi.org/10.1016/j.tcs.2009.02.018