Zulip Chat Archive
Stream: Is there code for X?
Topic: Iteration of a function which doesn't decrease values
Daniel Weber (Aug 26 2024 at 02:57):
Is this lemma in Mathlib?
lemma le_iterate_of_forall_le {α : Type*} [Preorder α] (f : α → α)
(hf : ∀ x, x ≤ f x) (x : α) (n : ℕ) :
x ≤ f^[n] x := by
induction n generalizing x
· simp
· trans f x
· apply hf
· simp only [iterate_succ, comp_apply, *]
I also need the corollary
lemma monotone_iterate_of_forall_le {α : Type*} [Preorder α] (f : α → α)
(hf : ∀ x, x ≤ f x) (x : α) :
Monotone (fun n ↦ f^[n] x)
Yury G. Kudryashov (Aug 26 2024 at 04:11):
@loogle Monotone, Nat.iterate, "id_le"
loogle (Aug 26 2024 at 04:11):
:search: Function.monotone_iterate_of_id_le
Daniel Weber (Aug 26 2024 at 04:12):
Thanks
Last updated: May 02 2025 at 03:31 UTC