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[Merged by Bors] - feat(analysis): Cauchy sequence and series lemmas #7858

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@PatrickMassot PatrickMassot commented Jun 9, 2021

from LTE. Mostly relaxing assumptions from metric to
pseudo-metric and proving some obvious lemmas.

eventually_constant_prod and eventually_constant_sum are duplicated by hand because to_additive gets confused by the appearance of 1.

In norm_le_zero_iff' {G : Type*} [semi_normed_group G] [separated_space G] and the following two lemmas the type classes assumptions look silly, but those lemmas are indeed useful in some specific situation in LTE.


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from LTE. Mostly relaxing assumptions from metric to
pseudo-metric and priving some obvious lemmas.
Co-authored-by: Eric Wieser <wieser.eric@gmail.com>
@PatrickMassot PatrickMassot added the awaiting-review The author would like community review of the PR label Jun 9, 2021
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riccardobrasca commented Jun 9, 2021

Is it reasonable to have something like metric.of_t2_pseudo_metric_space that produce normed_group G in presence of [semi_normed_group G] [separated_space G]? If the induced semi_normed_group structure is definitionally equal to the original one, then the lemmas for nomed_group should work to prove norm_eq_zero_iff' and friends.

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bors d+

src/analysis/normed_space/basic.lean Outdated Show resolved Hide resolved
src/analysis/normed_space/basic.lean Outdated Show resolved Hide resolved
variables [semi_normed_group α] {r C : ℝ} {f : ℕ → α}

lemma normed_group.cauchy_seq_of_le_geometric {C : ℝ} {r : ℝ} (hr : r < 1)
{u : ℕ → α} (h : ∀ n, ∥u n - u (n + 1)∥ ≤ C*r^n) : cauchy_seq u :=
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Suggested change
{u : ℕ → α} (h : ∀ n, ∥u n - u (n + 1)∥ ≤ C*r^n) : cauchy_seq u :=
{u : ℕ → α} (h : ∀ n, ∥u n - u (n + 1)∥ ≤ C*r^n) : cauchy_seq u :=

src/analysis/specific_limits.lean Outdated Show resolved Hide resolved
end

lemma normed_group.cauchy_series_of_le_geometric'' {C : ℝ} {u : ℕ → α} {N : ℕ} {r : ℝ}
(hr₀ : 0 < r) (hr₁ : r < 1)
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hr₀ seems useless here.

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I got tired of lemmas where most of the proof deals with weakening such constraint whereas they are never an issue when applying the lemma. Look at the previous lemma. Most of the proof is showing we can assume C and r are positive.

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bors bot commented Jun 10, 2021

✌️ PatrickMassot can now approve this pull request. To approve and merge a pull request, simply reply with bors r+. More detailed instructions are available here.

@github-actions github-actions bot added delegated The PR author may merge after reviewing final suggestions. and removed awaiting-review The author would like community review of the PR labels Jun 10, 2021
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bors merge

@github-actions github-actions bot added the ready-to-merge All that is left is for bors to build and merge this PR. (Remember you need to say `bors r+`.) label Jun 10, 2021
bors bot pushed a commit that referenced this pull request Jun 10, 2021
from LTE. Mostly relaxing assumptions from metric to
pseudo-metric and proving some obvious lemmas.

eventually_constant_prod and eventually_constant_sum are duplicated by hand because `to_additive` gets confused by the appearance of `1`.

In `norm_le_zero_iff' {G : Type*} [semi_normed_group G] [separated_space G]` and the following two lemmas the type classes assumptions look silly, but those lemmas are indeed useful in some specific situation in LTE.
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bors bot commented Jun 11, 2021

Build failed (retrying...):

bors bot pushed a commit that referenced this pull request Jun 11, 2021
from LTE. Mostly relaxing assumptions from metric to
pseudo-metric and proving some obvious lemmas.

eventually_constant_prod and eventually_constant_sum are duplicated by hand because `to_additive` gets confused by the appearance of `1`.

In `norm_le_zero_iff' {G : Type*} [semi_normed_group G] [separated_space G]` and the following two lemmas the type classes assumptions look silly, but those lemmas are indeed useful in some specific situation in LTE.
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bors bot commented Jun 11, 2021

This PR was included in a batch that was canceled, it will be automatically retried

bors bot pushed a commit that referenced this pull request Jun 11, 2021
from LTE. Mostly relaxing assumptions from metric to
pseudo-metric and proving some obvious lemmas.

eventually_constant_prod and eventually_constant_sum are duplicated by hand because `to_additive` gets confused by the appearance of `1`.

In `norm_le_zero_iff' {G : Type*} [semi_normed_group G] [separated_space G]` and the following two lemmas the type classes assumptions look silly, but those lemmas are indeed useful in some specific situation in LTE.
@bors
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bors bot commented Jun 11, 2021

Build failed (retrying...):

bors bot pushed a commit that referenced this pull request Jun 11, 2021
from LTE. Mostly relaxing assumptions from metric to
pseudo-metric and proving some obvious lemmas.

eventually_constant_prod and eventually_constant_sum are duplicated by hand because `to_additive` gets confused by the appearance of `1`.

In `norm_le_zero_iff' {G : Type*} [semi_normed_group G] [separated_space G]` and the following two lemmas the type classes assumptions look silly, but those lemmas are indeed useful in some specific situation in LTE.
bors bot pushed a commit that referenced this pull request Jun 11, 2021
from LTE. Mostly relaxing assumptions from metric to
pseudo-metric and proving some obvious lemmas.

eventually_constant_prod and eventually_constant_sum are duplicated by hand because `to_additive` gets confused by the appearance of `1`.

In `norm_le_zero_iff' {G : Type*} [semi_normed_group G] [separated_space G]` and the following two lemmas the type classes assumptions look silly, but those lemmas are indeed useful in some specific situation in LTE.
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bors bot commented Jun 11, 2021

Pull request successfully merged into master.

Build succeeded:

@bors bors bot changed the title feat(analysis): Cauchy sequence and series lemmas [Merged by Bors] - feat(analysis): Cauchy sequence and series lemmas Jun 11, 2021
@bors bors bot closed this Jun 11, 2021
@bors bors bot deleted the spe-lim branch June 11, 2021 19:07
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5 participants