@article{MZ_1936__41_168669,
     author = {Gr. Gentzen},
     title = {Die {Widerspruchsfreiheit} der {Stufenlogik}},
     journal = {Mathematische Zeitschrift},
     pages = {357--366},
     publisher = {mathdoc},
     volume = {41},
     year = {1936},
     zbl = {0015.19302},
     url = {http://geodesic.mathdoc.fr/item/MZ_1936__41_168669/}
}