@article{10_4153_CMB_1968_009_8,
     author = {Strang, Gilbert},
     title = {The {Nucleus} of a {Set}},
     journal = {Canadian mathematical bulletin},
     pages = {65--72},
     year = {1968},
     volume = {11},
     number = {1},
     doi = {10.4153/CMB-1968-009-8},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-1968-009-8/}
}