necessarily extensive) self-map. The identity mapping obviously has these two properties. Thus all complete lattices occur. Further results Besides the previous representation results, there are some other statements that can be made about complete lattices, or that take a particularly simple form in this case. An example is the Knaster–Tarski theorem, which states that the set of fixed points of a monotone function on a complete lattice is again a complete lattice. This is easily seen to be a generalization of the above observation about the images of increasing and idempotent functions, since these are instances of the theorem. See also lattice (order). References Closure operators Lattice theory