Order-closed topologies #
In this file we introduce 3 typeclass mixins that relate topology and order structures:
ClosedIicTopology
says that all the intervals $(-∞, a]$ (formally,Set.Iic a
) are closed sets;ClosedIciTopoplogy
says that all the intervals $[a, +∞)$ (formally,Set.Ici a
) are closed sets;OrderClosedTopology
says that the set of points(x, y)
such thatx ≤ y
is 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 ClosedIciTopoplogy
vs ClosedIicTopology,
Preordervs
PartialOrdervs
LinearOrder` etc)
see their statements.
Open / closed sets #
isOpen_lt
: iff
andg
are continuous functions, then{x | f x < g x}
is open;isOpen_Iio
,isOpen_Ioi
,isOpen_Ioo
: open intervals are open;isClosed_le
: iff
andg
are 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
: iff
converges toa
,g
converges tob
, and eventuallyf x ≤ g x
, thena ≤ b
le_of_tendsto
,ge_of_tendsto
: iff
converges toa
and 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
/max
of two continuous functions is continuous.Tendsto.min
,Tendsto.max
: iff
tends toa
andg
tends tob
, then their pointwisemin
/max
tend tomin a b
andmax 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
.
Alias of Filter.Tendsto.eventually_const_lt
.
Alias of Filter.Tendsto.eventually_const_le
.
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
.
Alias of Filter.Tendsto.eventually_lt_const
.
Alias of Filter.Tendsto.eventually_le_const
.
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 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.