@article{MS2_1963__12_165835,
     author = {Leif Kristensen},
     title = {On {Secondary} {Cohomology} {Operations.}},
     journal = {Mathematica Scandinavica},
     pages = {57--82},
     publisher = {mathdoc},
     volume = {12},
     year = {1963},
     zbl = {0118.18303},
     url = {http://geodesic.mathdoc.fr/item/MS2_1963__12_165835/}
}