@article{1093890707, author = {Satre, Thomas W.}, title = {Natural deduction rules for modal logics.}, journal = {Notre Dame J. Formal Logic}, volume = {13}, number = {3}, year = {1972}, pages = { 461-475}, language = {en}, url = {http://dml.mathdoc.fr/item/1093890707} }
Satre, Thomas W. Natural deduction rules for modal logics.. Notre Dame J. Formal Logic, Tome 13 (1972) no. 3, pp. 461-475. http://gdmltest.u-ga.fr/item/1093890707/