@article{MS2_1971__29_166207,
     author = {John Harper and Claude Schochet},
     title = {Coalgebra {Extensions} in {Two-Stage} {Postnikov} {Systems.}},
     journal = {Mathematica Scandinavica},
     pages = {232--236},
     publisher = {mathdoc},
     volume = {29},
     year = {1971},
     zbl = {0235.55019},
     url = {http://geodesic.mathdoc.fr/item/MS2_1971__29_166207/}
}