diff --git a/CHANGELOG.md b/CHANGELOG.md index 469c926af8..e29e5aec7b 100644 --- a/CHANGELOG.md +++ b/CHANGELOG.md @@ -196,6 +196,11 @@ Additions to existing modules record IsSuccessorSetMonomorphism (⟦_⟧ : N₁.Carrier → N₂.Carrier) : Set _ record IsSuccessorSetIsomorphism (⟦_⟧ : N₁.Carrier → N₂.Carrier) : Set _ +* In `Algebra.Properties.AbelianGroup`: + ``` + ⁻¹-anti-homo‿- : (x - y) ⁻¹ ≈ y - x + ``` + * In `Algebra.Properties.Group`: ```agda isQuasigroup : IsQuasigroup _∙_ _\\_ _//_ @@ -213,6 +218,8 @@ Additions to existing modules ⁻¹-selfInverse : SelfInverse _⁻¹ \\≗flip-//⇒comm : (∀ x y → x \\ y ≈ y // x) → Commutative _∙_ comm⇒\\≗flip-// : Commutative _∙_ → ∀ x y → x \\ y ≈ y // x + ⁻¹-anti-homo-// : (x // y) ⁻¹ ≈ y // x + ⁻¹-anti-homo-\\ : (x \\ y) ⁻¹ ≈ y \\ x ``` * In `Algebra.Properties.Loop`: diff --git a/src/Algebra/Properties/AbelianGroup.agda b/src/Algebra/Properties/AbelianGroup.agda index 87c6b7c6b9..b5eb290081 100644 --- a/src/Algebra/Properties/AbelianGroup.agda +++ b/src/Algebra/Properties/AbelianGroup.agda @@ -23,6 +23,9 @@ open import Algebra.Properties.Group group public ------------------------------------------------------------------------ -- Properties of abelian groups +⁻¹-anti-homo‿- : ∀ x y → (x - y) ⁻¹ ≈ y - x +⁻¹-anti-homo‿- = ⁻¹-anti-homo-// + xyx⁻¹≈y : ∀ x y → x ∙ y ∙ x ⁻¹ ≈ y xyx⁻¹≈y x y = begin x ∙ y ∙ x ⁻¹ ≈⟨ ∙-congʳ $ comm _ _ ⟩ diff --git a/src/Algebra/Properties/Group.agda b/src/Algebra/Properties/Group.agda index 3d4a7d7713..bac2c84d31 100644 --- a/src/Algebra/Properties/Group.agda +++ b/src/Algebra/Properties/Group.agda @@ -126,6 +126,22 @@ inverseʳ-unique x y eq = trans (y≈x\\z x y ε eq) (identityʳ _) (x ∙ y) ∙ y ⁻¹ ∙ x ⁻¹ ≈⟨ assoc (x ∙ y) (y ⁻¹) (x ⁻¹) ⟩ x ∙ y ∙ (y ⁻¹ ∙ x ⁻¹) ∎ +⁻¹-anti-homo-// : ∀ x y → (x // y) ⁻¹ ≈ y // x +⁻¹-anti-homo-// x y = begin + (x // y) ⁻¹ ≡⟨⟩ + (x ∙ y ⁻¹) ⁻¹ ≈⟨ ⁻¹-anti-homo-∙ x (y ⁻¹) ⟩ + (y ⁻¹) ⁻¹ ∙ x ⁻¹ ≈⟨ ∙-congʳ (⁻¹-involutive y) ⟩ + y ∙ x ⁻¹ ≡⟨⟩ + y // x ∎ + +⁻¹-anti-homo-\\ : ∀ x y → (x \\ y) ⁻¹ ≈ y \\ x +⁻¹-anti-homo-\\ x y = begin + (x \\ y) ⁻¹ ≡⟨⟩ + (x ⁻¹ ∙ y) ⁻¹ ≈⟨ ⁻¹-anti-homo-∙ (x ⁻¹) y ⟩ + y ⁻¹ ∙ (x ⁻¹) ⁻¹ ≈⟨ ∙-congˡ (⁻¹-involutive x) ⟩ + y ⁻¹ ∙ x ≡⟨⟩ + y \\ x ∎ + \\≗flip-//⇒comm : (∀ x y → x \\ y ≈ y // x) → Commutative _∙_ \\≗flip-//⇒comm \\≗//ᵒ x y = begin x ∙ y ≈⟨ ∙-congˡ (//-rightDividesˡ x y) ⟨