Tidy up groups (#64)

Groups/Subgroups/Definition.agda

@@ -0,0 +1,18 @@
+{-# 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 Groups.Homomorphisms.Definition
+
+module Groups.Subgroups.Definition where
+
+record Subgroup {a} {b} {c} {d} {A : Set a} {B : Set c} {S : Setoid {a} {b} A} {T : Setoid {c} {d} B} {_·A_ : A → A → A} {_·B_ : B → B → B} (G : Group S _·A_) (H : Group T _·B_) {f : B → A} (hom : GroupHom H G f) : Set (a ⊔ b ⊔ c ⊔ d) where
+  open Setoid T renaming (_∼_ to _∼G_)
+  open Setoid S renaming (_∼_ to _∼H_)
+  field
+    fInj : SetoidInjection T S f