@article{1183732304, author = {Copi, Irving M.}, title = {Another Variant of Natural Deduction}, journal = {J. Symbolic Logic}, volume = {21}, number = {1}, year = {1956}, pages = { 52-55}, language = {en}, url = {http://dml.mathdoc.fr/item/1183732304} }
Copi, Irving M. Another Variant of Natural Deduction. J. Symbolic Logic, Tome 21 (1956) no. 1, pp. 52-55. http://gdmltest.u-ga.fr/item/1183732304/