Petr Hájek, Vítezslav Svejdar. A note on the normal form of closed formulas of interpretability logic. Studia Logica, 50(1):25-28, 1991. [doi]
@article{HajekS91,
title = {A note on the normal form of closed formulas of interpretability logic},
author = {Petr Hájek and Vítezslav Svejdar},
year = {1991},
doi = {10.1007/BF00370384},
url = {http://dx.doi.org/10.1007/BF00370384},
researchr = {https://researchr.org/publication/HajekS91},
cites = {0},
citedby = {0},
journal = {Studia Logica},
volume = {50},
number = {1},
pages = {25-28},
}