Skip to content

[Merged by Bors] - feat: if Y = f(X) then Y is X-measurable #39728

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Closed
mathlib-splicebot wants to merge 2 commits into from
Closed

[Merged by Bors] - feat: if Y = f(X) then Y is X-measurable #39728

Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
eac137e
Automated addition of changes in Mathlib/MeasureTheory/MeasurableSpac…
EtienneC30 May 22, 2026
ebc70c2
Update Mathlib/MeasureTheory/MeasurableSpace/Basic.lean
EtienneC30 May 28, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
8 changes: 8 additions & 0 deletions Mathlib/MeasureTheory/MeasurableSpace/Basic.lean
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -183,6 +183,14 @@ theorem measurable_iff_comap_le {m₁ : MeasurableSpace α} {m₂ : MeasurableSp

alias ⟨Measurable.comap_le, Measurable.of_comap_le⟩ := measurable_iff_comap_le

/-- If `g = h ∘ f`, then the sigma-algebra generated by `g` is
smaller than the one generated by `f`. -/
lemma MeasurableSpace.comap_le_comap_of_eq_comp {mβ : MeasurableSpace β} {mγ : MeasurableSpace γ}
{f : α → β} {g : α → γ} (h : β → γ) (mh : Measurable h) (heq : g = h ∘ f) :
mγ.comap g ≤ mβ.comap f := by
rw [heq, ← MeasurableSpace.comap_comp]
exact MeasurableSpace.comap_mono mh.comap_le

theorem comap_measurable {m : MeasurableSpace β} (f : α → β) : Measurable[m.comap f] f :=
fun s hs => ⟨s, hs, rfl⟩

Expand Down
Loading