Order-closed topologies #
In this file we introduce 3 typeclass mixins that relate topology and order structures:
ClosedIicTopologysays that all the intervals $(-∞, a]$ (formally,Set.Iic a) are closed sets;ClosedIciTopologysays that all the intervals $[a, +∞)$ (formally,Set.Ici a) are closed sets;OrderClosedTopologysays that the set of points(x, y)such thatx ≤ yis closed in the product topology.
The last predicate implies the first two.
We prove many basic properties of such topologies.
Main statements #
This file contains the proofs of the following facts.
For exact requirements
(OrderClosedTopology vs ClosedIciTopology vs ClosedIicTopology, PreordervsPartialOrdervsLinearOrder` etc)
see their statements.
Open / closed sets #
isOpen_lt: iffandgare continuous functions, then{x | f x < g x}is open;isOpen_Iio,isOpen_Ioi,isOpen_Ioo: open intervals are open;isClosed_le: iffandgare continuous functions, then{x | f x ≤ g x}is closed;isClosed_Iic,isClosed_Ici,isClosed_Icc: closed intervals are closed;frontier_le_subset_eq,frontier_lt_subset_eq: frontiers of both{x | f x ≤ g x}and{x | f x < g x}are included by{x | f x = g x};
Convergence and inequalities #
le_of_tendsto_of_tendsto: iffconverges toa,gconverges tob, and eventuallyf x ≤ g x, thena ≤ ble_of_tendsto,ge_of_tendsto: iffconverges toaand eventuallyf x ≤ b(resp.,b ≤ f x), thena ≤ b(resp.,b ≤ a); we also provide primed versions that assume the inequalities to hold for allx.
Min, max, sSup and sInf #
Continuous.min,Continuous.max: pointwisemin/maxof two continuous functions is continuous.Tendsto.min,Tendsto.max: ifftends toaandgtends tob, then their pointwisemin/maxtend tomin a bandmax a b, respectively.
If α is a topological space and a preorder, ClosedIicTopology α means that Iic a is
closed for all a : α.
For any
a, the set(-∞, a]is closed.
Instances
If α is a topological space and a preorder, ClosedIciTopology α means that Ici a is
closed for all a : α.
For any
a, the set[a, +∞)is closed.
Instances
A topology on a set which is both a topological space and a preorder is order-closed if the
set of points (x, y) with x ≤ y is closed in the product space. We introduce this as a mixin.
This property is satisfied for the order topology on a linear order, but it can be satisfied more
generally, and suffices to derive many interesting properties relating order and topology.
The set
{ (x, y) | x ≤ y }is a closed set.
Instances
Alias of the reverse direction of bddAbove_closure.
Left neighborhoods on a ClosedIicTopology #
Limits to the left of real functions are defined in terms of neighborhoods to the left,
either open or closed, i.e., members of 𝓝[<] a and 𝓝[≤] a.
Here we prove that all left-neighborhoods of a point are equal,
and we prove other useful characterizations which require the stronger hypothesis OrderTopology α
in another file.
Point excluded #
Point included #
Alias of the reverse direction of bddBelow_closure.
Right neighborhoods on a ClosedIciTopology #
Limits to the right of real functions are defined in terms of neighborhoods to the right,
either open or closed, i.e., members of 𝓝[>] a and 𝓝[≥] a.
Here we prove that all right-neighborhoods of a point are equal,
and we prove other useful characterizations which require the stronger hypothesis OrderTopology α
in another file.
Point excluded #
Point included #
Alias of le_of_tendsto_of_tendsto.
If s is a closed set and two functions f and g are continuous on s,
then the set {x ∈ s | f x ≤ g x} is a closed set.
The set of monotone functions on a set is closed.
The set of monotone functions is closed.
The set of antitone functions on a set is closed.
The set of antitone functions is closed.
The only order closed topology on a linear order which is a PredOrder and a SuccOrder
is the discrete topology.
This theorem is not an instance,
because it causes searches for PredOrder and SuccOrder with their Preorder arguments
and very rarely matches.