Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

[Merged by Bors] - feat(group_theory/subgroup/basic): Contrapositive of card_le_one_iff_eq_bot #9918

Closed
wants to merge 1 commit into from
Closed

[Merged by Bors] - feat(group_theory/subgroup/basic): Contrapositive of card_le_one_iff_eq_bot #9918

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Jump to
Jump to file
Failed to load files.
Diff view
Diff view
3 changes: 3 additions & 0 deletions src/group_theory/subgroup/basic.lean
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -479,6 +479,9 @@ end
(λ x hx, by simpa [subtype.ext_iff] using fintype.card_le_one_iff.1 h ⟨x, hx⟩ 1),
λ h, by simp [h]⟩

@[to_additive] lemma one_lt_card_iff_ne_bot [fintype H] : 1 < fintype.card H ↔ H ≠ ⊥ :=
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I was curious what to_additive does with the naming on things like this, and it turns out, it's not great. Not a problem for this PR, but I'll open an issue.

lt_iff_not_ge'.trans (not_iff_not.mpr H.card_le_one_iff_eq_bot)

/-- The inf of two subgroups is their intersection. -/
@[to_additive "The inf of two `add_subgroups`s is their intersection."]
instance : has_inf (subgroup G) :=
Expand Down