Zulip Chat Archive
Stream: mathlib4
Topic: Direct product of subgroups is abelian
Move fast (Apr 18 2025 at 15:10):
import Mathlib
open Subgroup
variable {n : ℕ}
variable {G : Fin n → Type*} [∀ i, Group (G i)]
instance (h:CommGroup (Π i : Fin n, G i) ) :
∀ i : Fin n, CommGroup (G i) := by sorry
How can I construct this instance? I want to show that if the direct product of subgroups is abelian, then every direct factor is abelian.
Aaron Liu (Apr 18 2025 at 15:14):
I don't think this is provable this is provable, but needs some kind of choice
Aaron Liu (Apr 18 2025 at 15:14):
Since that statement doesn't mean what you say it does
Move fast (Apr 18 2025 at 15:19):
I have modified the edited content.
Aaron Liu (Apr 18 2025 at 15:22):
It is still not provable, and still does not say what you think it says
Aaron Liu (Apr 18 2025 at 15:22):
Maybe you can use docs#IsMulCommutative instead
Move fast (Apr 18 2025 at 15:27):
ok, thank you.
Kevin Buzzard (Apr 18 2025 at 15:43):
As I already told you once @Move fast , CommGroup X
does not mean "the group X is commutative".
Kevin Buzzard (Apr 18 2025 at 15:43):
It is the type of commutative group structures on X.
Last updated: May 02 2025 at 03:31 UTC