@article{GDZPPN002057174, title = {Essential and inessential complexes.}, journal = {Commentarii mathematici Helvetici}, volume = {33}, year = {1959}, pages = {70-80}, zbl = {0178.26201}, url = {http://dml.mathdoc.fr/item/GDZPPN002057174} }
Bertsein, Israel. Essential and inessential complexes.. Commentarii mathematici Helvetici, Tome 33 (1959) pp. 70-80. http://gdmltest.u-ga.fr/item/GDZPPN002057174/