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 : }

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