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 that- x ≤ 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: if- fand- gare continuous functions, then- {x | f x < g x}is open;
- isOpen_Iio,- isOpen_Ioi,- isOpen_Ioo: open intervals are open;
- isClosed_le: if- fand- gare 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: if- fconverges to- a,- gconverges to- b, and eventually- f x ≤ g x, then- a ≤ b
- le_of_tendsto,- ge_of_tendsto: if- fconverges to- aand eventually- f x ≤ b(resp.,- b ≤ f x), then- a ≤ b(resp.,- b ≤ a); we also provide primed versions that assume the inequalities to hold for all- x.
Min, max, sSup and sInf #
- Continuous.min,- Continuous.max: pointwise- min/- maxof two continuous functions is continuous.
- Tendsto.min,- Tendsto.max: if- ftends to- aand- gtends to- b, then their pointwise- min/- maxtend to- min a band- max 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.