@article{10_1090_S0894_0347_1990_1071116_6,
     author = {Friedman, Sy D.},
     title = {The {\ensuremath{\Pi}{\textonesuperior}₂-singleton} conjecture},
     journal = {Journal of the American Mathematical Society},
     pages = {771--791},
     year = {1990},
     volume = {03},
     number = {4},
     doi = {10.1090/S0894-0347-1990-1071116-6},
     url = {http://geodesic.mathdoc.fr/articles/10.1090/S0894-0347-1990-1071116-6/}
}