@article{10_4153_CJM_1972_119_8,
     author = {Harris, Douglas},
     title = {Extension {Closed} and {Cluster} {Closed} {Subspaces}},
     journal = {Canadian journal of mathematics},
     pages = {1132--1136},
     year = {1972},
     volume = {24},
     number = {6},
     doi = {10.4153/CJM-1972-119-8},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1972-119-8/}
}