@article{ZR_1977_2_10_a8,
     author = {R. P. Nederpelt},
     title = {Presentation of {Natural} {Deduction}},
     journal = {Zbornik radova},
     pages = {115 },
     year = {1977},
     volume = {2},
     number = {10},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/ZR_1977_2_10_a8/}
}