\bibitem{CousotCousot-PORTM79-38-2} P{.} Cousot and R{.} Cousot. \newblock A constructive characterization of the lattices of all retractions, pre-closure, quasi-closure and closure operators on a complete lattice. \newblock \emph{Portugali\ae\ Mathematica}, 38(2):185--198, 1979. @article{CousotCousot-PORTM79-38-2, author = {Cousot, P{.} and Cousot, R{.}}, title = {A constructive characterization of the lattices of all retractions, pre-closure, quasi-closure and closure operators on a complete lattice}, journal = {Portugali\ae\ Mathematica}, volume = 38, number = 2, pages = {185--198}, year = 1979, }