@article{MZM_1979_26_4_a1,
     author = {Yu. G. Penzin},
     title = {Twins problem in formal arithmetic},
     journal = {Matemati\v{c}eskie zametki},
     pages = {505--511},
     publisher = {mathdoc},
     volume = {26},
     number = {4},
     year = {1979},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1979_26_4_a1/}
}