@article{MOMA_1965__69_177296,
     author = {Z. Hedrlin and A. Pultr},
     title = {Symmetric {Relations} {(Undirected} {Graphs)} with {Given} {Semigroups.}},
     journal = {Monatshefte f\"ur Mathematik},
     pages = {318--322},
     publisher = {mathdoc},
     volume = {69},
     year = {1965},
     zbl = {0139.24803},
     url = {http://geodesic.mathdoc.fr/item/MOMA_1965__69_177296/}
}