@article{10_4153_CJM_1987_025_1,
     author = {Hell, Pavol and Rival, Ivan},
     title = {Absolute {Retracts} and {Varieties} of {Reflexive} {Graphs}},
     journal = {Canadian journal of mathematics},
     pages = {544--567},
     year = {1987},
     volume = {39},
     number = {3},
     doi = {10.4153/CJM-1987-025-1},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1987-025-1/}
}