@article{RSMUP_1990__83__133_0,
     author = {Loonstra, F.},
     title = {Pseudo-closure-operators},
     journal = {Rendiconti del Seminario Matematico della Universit\`a di Padova},
     pages = {133--137},
     publisher = {Seminario Matematico of the University of Padua},
     volume = {83},
     year = {1990},
     mrnumber = {1066434},
     zbl = {0719.16002},
     language = {en},
     url = {http://www.numdam.org/item/RSMUP_1990__83__133_0/}
}