@article{MOMA_1964__68_177266,
     author = {Z. Hedrlin and A. Pultr},
     title = {Relations {(Graphs)} with {Given} {Infinite} {Semigroups.}},
     journal = {Monatshefte f\"ur Mathematik},
     pages = {421--425},
     publisher = {mathdoc},
     volume = {68},
     year = {1964},
     zbl = {0139.24802},
     url = {http://geodesic.mathdoc.fr/item/MOMA_1964__68_177266/}
}