@article{JAC_2005__21_2_a1,
     author = {Haemers, Willem H.},
     title = {Conditions for singular incidence matrices},
     journal = {Journal of Algebraic Combinatorics},
     pages = {179--183},
     publisher = {mathdoc},
     volume = {21},
     number = {2},
     year = {2005},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/JAC_2005__21_2_a1/}
}