Filter.atTop and Filter.atBot filters on preorders, monoids and groups. #
In this file we define the filters
Filter.atTop: corresponds ton → +∞;Filter.atBot: corresponds ton → -∞.
Then we prove many lemmas like “if f → +∞, then f ± c → +∞”.
atTop is the filter representing the limit → ∞ on an ordered set.
It is generated by the collection of up-sets {b | a ≤ b}.
(The preorder need not have a top element for this to be well defined,
and indeed is trivial when a top element exists.)
Equations
- Filter.atTop = ⨅ (a : α), Filter.principal (Set.Ici a)
Instances For
atBot is the filter representing the limit → -∞ on an ordered set.
It is generated by the collection of down-sets {b | b ≤ a}.
(The preorder need not have a bottom element for this to be well defined,
and indeed is trivial when a bottom element exists.)
Equations
- Filter.atBot = ⨅ (a : α), Filter.principal (Set.Iic a)
Instances For
Equations
- ⋯ = inst
Equations
- ⋯ = inst
Alias of the forward direction of Filter.eventually_atTop.
Alias of the forward direction of Filter.eventually_atBot.
Sequences #
If u is a sequence which is unbounded above,
then after any point, it reaches a value strictly greater than all previous values.
If u is a sequence which is unbounded below,
then after any point, it reaches a value strictly smaller than all previous values.
If u is a sequence which is unbounded above,
then it Frequently reaches a value strictly greater than all previous values.
If u is a sequence which is unbounded below,
then it Frequently reaches a value strictly smaller than all previous values.
A function f grows to +∞ independent of an order-preserving embedding e.
Alias of Filter.tendsto_atTop_atTop_of_monotone.
Alias of Filter.tendsto_atBot_atBot_of_monotone.
A function f goes to -∞ independent of an order-preserving embedding e.
If f is a monotone sequence of Finsets and each x belongs to one of f n, then
Tendsto f atTop atTop.
Alias of Filter.tendsto_atTop_finset_of_monotone.
If f is a monotone sequence of Finsets and each x belongs to one of f n, then
Tendsto f atTop atTop.
A function f maps upwards closed sets (atTop sets) to upwards closed sets when it is a
Galois insertion. The Galois "insertion" and "connection" is weakened to only require it to be an
insertion and a connection above b.
A function f maps upwards closed sets (atTop sets) to upwards closed sets when it is a
Galois insertion. The Galois "insertion" and "connection" is weakened to only require it to be an
insertion and a connection above b.
The image of the filter atTop on Ici a under the coercion equals atTop.
The image of the filter atTop on Ioi a under the coercion equals atTop.
The atTop filter for an open interval Ioi a comes from the atTop filter in the ambient
order.
The atTop filter for an open interval Ici a comes from the atTop filter in the ambient
order.
The atBot filter for an open interval Iio a comes from the atBot filter in the ambient
order.
The atBot filter for an open interval Iio a comes from the atBot filter in the ambient
order.
The atBot filter for an open interval Iic a comes from the atBot filter in the ambient
order.
The atBot filter for an open interval Iic a comes from the atBot filter in the ambient
order.
If u is a monotone function with linear ordered codomain and the range of u is not bounded
above, then Tendsto u atTop atTop.
If u is a monotone function with linear ordered codomain and the range of u is not bounded
below, then Tendsto u atBot atBot.
If a monotone function u : ι → α tends to atTop along some non-trivial filter l, then
it tends to atTop along atTop.
If a monotone function u : ι → α tends to atBot along some non-trivial filter l, then
it tends to atBot along atBot.
Given an antitone basis s : ℕ → Set α of a filter, extract an antitone subbasis s ∘ φ,
φ : ℕ → ℕ, such that m < n implies r (φ m) (φ n). This lemma can be used to extract an
antitone basis with basis sets decreasing "sufficiently fast".
If f is a nontrivial countably generated filter, then there exists a sequence that converges
to f.
An abstract version of continuity of sequentially continuous functions on metric spaces:
if a filter k is countably generated then Tendsto f k l iff for every sequence u
converging to k, f ∘ u tends to l.
A sequence converges if every subsequence has a convergent subsequence.