@article{CM_1969__21_3_312_0,
     author = {Henderson, David W.},
     title = {Open subsets of {Hilbert} space},
     journal = {Compositio Mathematica},
     pages = {312--318},
     publisher = {Wolters-Noordhoff Publishing},
     volume = {21},
     number = {3},
     year = {1969},
     mrnumber = {251748},
     zbl = {0179.52102},
     language = {en},
     url = {http://archive.numdam.org/item/CM_1969__21_3_312_0/}
}