@article{10_4064_am_21_3_449_453,
     author = {H. Brzeskwiniewicz},
     title = {Latent roots and off-diagonal elements of the association matrix in {PBIB} designs and the number of associate classes},
     journal = {Applicationes Mathematicae},
     pages = {449--453},
     publisher = {mathdoc},
     volume = {21},
     number = {3},
     year = {1991},
     doi = {10.4064/am-21-3-449-453},
     zbl = {0753.62042},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/am-21-3-449-453/}
}