@article{MZ_1952__57_169302,
     author = {Georg Kreisel},
     title = {Some concepts concerning formal systems on number theory.},
     journal = {Mathematische Zeitschrift},
     pages = {1--12},
     publisher = {mathdoc},
     volume = {57},
     year = {1952},
     zbl = {0048.24702},
     url = {http://geodesic.mathdoc.fr/item/MZ_1952__57_169302/}
}