@article{10_4153_CMB_1980_070_0,
     author = {Martin, Harold W.},
     title = {Derived {Subspaces} of {Metric} {Spaces}},
     journal = {Canadian mathematical bulletin},
     pages = {465--467},
     year = {1980},
     volume = {23},
     number = {4},
     doi = {10.4153/CMB-1980-070-0},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-1980-070-0/}
}