diff --git a/src/models.rs b/src/models.rs
index d0ca964..942cc8d 100644
--- a/src/models.rs
+++ b/src/models.rs
@@ -10,6 +10,11 @@ struct VertexIncidenceHeader {
     first_incidence: Option<Incidence>,
 }
 
+struct IncidenceEntry {
+    next: Option<Incidence>,
+    neighbor: Vertex,
+}
+
 pub struct VertexNeighborIterator<'a> {
     graph: &'a Graph,
     incidence: Option<Incidence>,
@@ -20,8 +25,9 @@ impl<'a> Iterator for VertexNeighborIterator<'a> {
 
     fn next(&mut self) -> Option<Self::Item> {
         let incidence = self.incidence?;
-        self.incidence = self.graph.next_incidences[incidence.0];
-        Some(self.graph.incidence_vertices[incidence.0])
+        let entry = &self.graph.incidences[incidence.0];
+        self.incidence = entry.next;
+        Some(entry.neighbor)
     }
 }
 
@@ -32,30 +38,28 @@ impl<'a> Iterator for VertexNeighborIterator<'a> {
 // TODO: Add iterator of edges.
 pub struct Graph {
     // TODO: Index 'incidence_headers' by a 'Vertex' instead of 'Vertex.0'?
-    incidence_headers: Vec<VertexIncidenceHeader>,
-    next_incidences: Vec<Option<Incidence>>,
-    incidence_vertices: Vec<Vertex>,
+    vertices: Vec<VertexIncidenceHeader>,
+    incidences: Vec<IncidenceEntry>,
 }
 
 impl Graph {
     pub fn new() -> Graph {
         Graph {
-            incidence_headers: vec![],
-            next_incidences: vec![],
-            incidence_vertices: vec![],
+            vertices: vec![],
+            incidences: vec![],
         }
     }
 
     pub fn vertex_count(&self) -> usize {
-        self.incidence_headers.len()
+        self.vertices.len()
     }
 
     pub fn edge_count(&self) -> usize {
-        self.next_incidences.len() / 2
+        self.incidences.len() / 2
     }
 
     pub fn degree(&self, v: Vertex) -> usize {
-        self.incidence_headers[v.0].incidence_count
+        self.vertices[v.0].incidence_count
     }
 
     pub fn are_adjacent(&self, v1: Vertex, v2: Vertex) -> bool {
@@ -64,11 +68,11 @@ impl Graph {
 
     // TODO: 'fn add_vertex()' needs variants for custom vertex data.
     pub fn add_vertex(&mut self) -> Vertex {
-        self.incidence_headers.push(VertexIncidenceHeader {
+        self.vertices.push(VertexIncidenceHeader {
             incidence_count: 0,
             first_incidence: None,
         });
-        Vertex(self.incidence_headers.len() - 1)
+        Vertex(self.vertices.len() - 1)
     }
 
     // TODO: 'fn add_edge()' needs variants for custom edge data.
@@ -78,22 +82,22 @@ impl Graph {
     }
 
     fn add_incidence(&mut self, v1: Vertex, v2: Vertex) {
-        self.incidence_vertices.push(v2);
-        self.next_incidences
-            .push(self.incidence_headers[v1.0].first_incidence.take());
-        self.incidence_headers[v1.0].incidence_count += 1;
-        self.incidence_headers[v1.0].first_incidence =
-            Some(Incidence(self.incidence_vertices.len() - 1));
+        self.incidences.push(IncidenceEntry {
+            next: self.vertices[v1.0].first_incidence.take(),
+            neighbor: v2,
+        });
+        self.vertices[v1.0].incidence_count += 1;
+        self.vertices[v1.0].first_incidence = Some(Incidence(self.incidences.len() - 1));
     }
 
     pub fn vertices(&self) -> impl Iterator<Item = Vertex> {
-        (0..self.incidence_headers.len()).map(Vertex)
+        (0..self.vertices.len()).map(Vertex)
     }
 
     pub fn neighbors(&self, v: Vertex) -> impl Iterator<Item = Vertex> {
         VertexNeighborIterator {
             graph: self,
-            incidence: self.incidence_headers[v.0].first_incidence,
+            incidence: self.vertices[v.0].first_incidence,
         }
     }
 }