Tidy up groups (#64)

Groups/Abelian/Definition.agda

@@ -0,0 +1,17 @@
+{-# OPTIONS --safe --warning=error --without-K #-}
+
+open import LogicalFormulae
+open import Setoids.Setoids
+open import Functions
+open import Agda.Primitive using (Level; lzero; lsuc; _⊔_)
+open import Numbers.Naturals.Naturals
+open import Sets.FinSet
+open import Groups.Definition
+open import Sets.EquivalenceRelations
+
+module Groups.Abelian.Definition where
+
+record AbelianGroup {a} {b} {A : Set a} {S : Setoid {a} {b} A} {_·_ : A → A → A} (G : Group S _·_) : Set (lsuc a ⊔ b) where
+  open Setoid S
+  field
+    commutative : {a b : A} → (a · b) ∼ (b · a)