@article{10_1017_S2040618500033372,
     author = {Robertson, Alex. P. and Robertson, Wendy},
     title = {On {The} {Closed} {Graph} {Theorem}},
     journal = {Glasgow mathematical journal},
     pages = {9--12},
     year = {1956},
     volume = {2},
     number = {1},
     doi = {10.1017/S2040618500033372},
     url = {http://geodesic.mathdoc.fr/articles/10.1017/S2040618500033372/}
}