@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,
}