@article{10_21136_CMJ_1976_101434,
     author = {Butler, Kim Ki-Hang and Schwarz, \v{S}tefan},
     title = {The semigroup of circulant {Boolean} matrices},
     journal = {Czechoslovak Mathematical Journal},
     pages = {632--635},
     publisher = {mathdoc},
     volume = {26},
     number = {4},
     year = {1976},
     doi = {10.21136/CMJ.1976.101434},
     mrnumber = {0430121},
     zbl = {0347.20037},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.21136/CMJ.1976.101434/}
}