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feat(order/filter,topology/instances/nnreal): upgrade some lemmas to iff #18964

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@urkud urkud commented May 7, 2023

  • Add codisjoint.inf_left_sup_inf_right and is_compl.le_inf_sup_inf.
  • Add filter.comap_ite, filter.comap_max, and filter.tendsto_ite.
  • Add real.map_to_nnreal_at_top, real.comap_to_nnreal_at_top, and
    real.tendsto_to_nnreal_at_top_iff.
  • Rename tendsto_real_to_nnreal to filter.tendsto.real_to_nnreal
    so that it can be used with dot notation.
  • Add ennreal.tendsto_of_real_nhds_top.

I'm cleaning up old local branches. I don't remember why I wanted to
have these lemmas but IMHO upgrading from implications to iffs is a
good thing.

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@github-actions github-actions bot added the modifies-synchronized-file This PR touches a files that has already been ported to mathlib4, and may need a synchronization PR. label May 7, 2023
@urkud urkud added t-topology Topological spaces, uniform spaces, metric spaces, filters t-order Order hierarchy labels May 7, 2023
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@@ -320,6 +320,18 @@ calc a ⊓ x ≤ (b ⊔ y) ⊓ x : inf_le_inf hle le_rfl
lemma le_sup_right_iff_inf_left_le {a b} (h : is_compl x y) : a ≤ b ⊔ y ↔ a ⊓ x ≤ b :=
⟨h.inf_left_le_of_le_sup_right, h.symm.dual.inf_left_le_of_le_sup_right⟩

lemma sup_inf_sup_eq (h : is_compl x y) : (a ⊔ x) ⊓ (b ⊔ y) = (b ⊓ x) ⊔ (a ⊓ y) :=
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I think sup_inf_sup_comm is the standard name for this type of thing, though usually we'd order it as

Suggested change
lemma sup_inf_sup_eq (h : is_compl x y) : (a ⊔ x) ⊓ (by) = (bx) ⊔ (ay) :=
lemma sup_inf_sup_comm (h : is_compl a d) : (a ⊔ b) ⊓ (cd) = (ac) ⊔ (bd) :=

Maybe it's convenient to have both

@semorrison semorrison added the awaiting-author A reviewer has asked the author a question or requested changes label Jun 5, 2023
@semorrison semorrison added the too-late This PR was ready too late for inclusion in mathlib3 label Jul 16, 2023
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awaiting-author A reviewer has asked the author a question or requested changes modifies-synchronized-file This PR touches a files that has already been ported to mathlib4, and may need a synchronization PR. t-order Order hierarchy t-topology Topological spaces, uniform spaces, metric spaces, filters too-late This PR was ready too late for inclusion in mathlib3
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