Gao, Feng, and George Tourlakis. “A Short and Readable Proof of Cut Elimination for Two First-Order Modal Logics”. Bulletin of the Section of Logic 44, no. 3/4 (January 1, 2015): 131–147. Accessed May 13, 2024. https://czasopisma.uni.lodz.pl/bulletin/article/view/16229.