@article{MOMA_1978__85_177849,
     author = {P. Hell and J. Nesetril},
     title = {Homomorphisms of {Graphs} and of {Their} {Orientations.}},
     journal = {Monatshefte f\"ur Mathematik},
     pages = {39--48},
     publisher = {mathdoc},
     volume = {85},
     year = {1978},
     zbl = {0375.05023},
     url = {http://geodesic.mathdoc.fr/item/MOMA_1978__85_177849/}
}