Zulip Chat Archive
Stream: Is there code for X?
Topic: injection of range of a composition
Nir Paz (Aug 07 2024 at 10:54):
Do we have this?
import Mathlib
example {α β γ} (f : α → β) (g : β → γ) : Nonempty (Set.range (g ∘ f) ↪ Set.range f) := sorry
Eric Wieser (Aug 07 2024 at 11:44):
This works:
example {α β γ} (f : α → β) (g : β → γ) : Nonempty (Set.range (g ∘ f) ↪ Set.range f) := by
rw [← Cardinal.lift_mk_le, Set.range_comp]
exact Cardinal.mk_image_le_lift.trans_eq <| congr_fun Cardinal.lift_umax'.symm _
Nir Paz (Aug 07 2024 at 12:09):
Thanks!
Last updated: May 02 2025 at 03:31 UTC