@article{10_4153_CJM_1966_121_7,
     author = {Hedrl{\'\i}n, Z. and Pultr, A.},
     title = {On {Rigid} {Undirected} {Graphs}},
     journal = {Canadian journal of mathematics},
     pages = {1237--1242},
     year = {1966},
     volume = {18},
     number = {1},
     doi = {10.4153/CJM-1966-121-7},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1966-121-7/}
}