@article{10_21136_CMJ_1970_100967,
     author = {Clifford, Alfred Hoblitzelle and Miller, D. D.},
     title = {Union and symmetry preserving endomorphisms of the semigroup of all binary relations on a set},
     journal = {Czechoslovak Mathematical Journal},
     pages = {303--314},
     publisher = {mathdoc},
     volume = {20},
     number = {2},
     year = {1970},
     doi = {10.21136/CMJ.1970.100967},
     mrnumber = {0262395},
     zbl = {0205.01901},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.21136/CMJ.1970.100967/}
}