Open And Closed Maps
In topology, an open map is a function between two topological spaces which maps open sets to open sets. That is, a function f : X → Y is open if for any open set U in X, the image f(U) is open in Y. Likewise, a closed map is a function which maps closed sets to closed sets. (The concept of a closed map should not be confused with that of a closed operator.)
Neither open nor closed maps are required to be continuous. Although their definitions seem more natural, open and closed maps are much less important than continuous maps. Recall that, by definition, a function f : X → Y is continuous if the preimage of every open set of Y is open in X. (Equivalently, if the preimage of every closed set of Y is closed in X).
Read more about Open And Closed Maps: Examples, Properties, Open and Closed Mapping Theorems
Famous quotes containing the words open and, open, closed and/or maps:
“Meanwhile Snow White held court,
rolling her china-blue doll eyes open and shut
and sometimes referring to her mirror
as women do.”
—Anne Sexton (1928–1974)
“It is open to a war resister to judge between the combatants and wish success to the one who has justice on his side. By so judging he is more likely to bring peace between the two than by remaining a mere spectator.”
—Mohandas K. Gandhi (1869–1948)
“My old Father used to have a saying that “If you make a bad bargain, hug it the tighter”; and it occurs to me, that if the bargain you have just closed [marriage] can possibly be called a bad one, it is certainly the most pleasant one for applying that maxim to, which my fancy can, by any effort, picture.”
—Abraham Lincoln (1809–1865)
“Living in cities is an art, and we need the vocabulary of art, of style, to describe the peculiar relationship between man and material that exists in the continual creative play of urban living. The city as we imagine it, then, soft city of illusion, myth, aspiration, and nightmare, is as real, maybe more real, than the hard city one can locate on maps in statistics, in monographs on urban sociology and demography and architecture.”
—Jonathan Raban (b. 1942)