@article{CMH_1959__33_139164,
     author = {Israel Bertsein},
     title = {Essential and inessential complexes.},
     journal = {Commentarii mathematici Helvetici},
     pages = {70--80},
     publisher = {mathdoc},
     volume = {33},
     year = {1959},
     zbl = {0178.26201},
     url = {http://geodesic.mathdoc.fr/item/CMH_1959__33_139164/}
}