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