diff --git a/graph/digraph.h b/graph/digraph.h
index 0c3bcaf..21dba0c 100644
--- a/graph/digraph.h
+++ b/graph/digraph.h
@@ -4,8 +4,6 @@
 #include "graph.h"
 #include "algorithm/breadth_first_search.h"
 
-#include <ranges>
-
 namespace graph {
 
 template<typename T>
@@ -26,9 +24,6 @@ public:
 
   // Reverse graph directions
   auto reverse();
-
-  // Return vertices
-  auto vertices();
 };
 
 template<typename T>
@@ -56,7 +51,7 @@ template<typename T>
 auto Digraph<T>::reverse() {
   std::map<T, std::set<T>> revMatrix;
   
-  for (const auto& u : vertices()) {
+  for (const auto& u : this->vertices()) {
     for (const auto& v : this->adjMatrix[u]) {
       revMatrix[v].insert(u);
     }
@@ -65,11 +60,6 @@ auto Digraph<T>::reverse() {
   return revMatrix;
 }
 
-template<typename T>
-auto Digraph<T>::vertices() {
-  return std::views::keys(this->adjMatrix);
-}
-
 } // namespace graph
 
 #endif
\ No newline at end of file
diff --git a/graph/graph.h b/graph/graph.h
index e67bd27..7b7738b 100644
--- a/graph/graph.h
+++ b/graph/graph.h
@@ -4,6 +4,7 @@
 #include <map>
 #include <set>
 #include <ostream>
+#include <ranges>
 
 namespace graph {
 
@@ -17,13 +18,16 @@ public:
   ~Graph();
   
   // Return true if there is a path from u to v
-  virtual bool contains(const T& u, const T& v) = 0;
+  virtual bool contains(const T& u, const T& v) =0;
 
   // Add edge e(u,v)
-  virtual void insert(const T& u, const T& v) = 0;
+  virtual void insert(const T& u, const T& v) =0;
 
   // Remove edge e(u,v)
-  virtual void remove(const T& u, const T& v) = 0;
+  virtual void remove(const T& u, const T& v) =0;
+
+  // Return graph vertices
+  auto vertices();
 
   // Return num. of vertices
   std::uint16_t V();
@@ -42,6 +46,11 @@ Graph<T>::~Graph() {
   adjMatrix.clear();
 }
 
+template<typename T>
+auto Graph<T>::vertices() {
+  return std::views::keys(adjMatrix);
+}
+
 template<typename T>
 std::uint16_t Graph<T>::V() {
   return static_cast<std::uint16_t>(adjMatrix.size());
@@ -50,8 +59,8 @@ std::uint16_t Graph<T>::V() {
 template<typename T>
 std::uint16_t Graph<T>::E() {
   std::uint16_t edges = 0;
-  for (const auto& v : adjMatrix) {
-    edges += static_cast<std::uint16_t>(v.second.size());
+  for (const auto& u : vertices()) {
+    edges += static_cast<std::uint16_t>(adjMatrix[u].size());
   }
   return static_cast<std::uint16_t>(edges);
 }
@@ -59,10 +68,10 @@ std::uint16_t Graph<T>::E() {
 template<typename T>
 std::ostream& operator<<(std::ostream& os, Graph<T>& G) {
   os << "V: " << G.V() << " E: " << G.E() << '\n';
-  for (const auto& u : G.adjMatrix) {
-    if (!u.second.empty()) {
-      for (const auto& v : u.second) {
-        os << u.first << "->" << v << ' ';
+  for (const auto& u : this->vertices()) {
+    if (!this->adjMatrix[u].empty()) {
+      for (const auto& v : this->adjMatrix[u]) {
+        os << u << "->" << v << ' ';
       }
       os << '\n';
     }
diff --git a/test/graph_test.cc b/test/graph_test.cc
index 01fc995..9b7bc89 100644
--- a/test/graph_test.cc
+++ b/test/graph_test.cc
@@ -35,7 +35,7 @@ TEST_SUITE("Graph") {
     G.insert(13, 9);
     G.insert(12, 10);
 
-    REQUIRE_EQ(G.adjMatrix.size(), 13);
+    REQUIRE_EQ(G.V(), 13);
 
     auto reverse = G.reverse();
 
@@ -85,8 +85,6 @@ TEST_SUITE("Graph") {
     G.insert(13, 9);
     G.insert(12, 10);
 
-    REQUIRE_EQ(G.adjMatrix.size(), 13);
-
     CHECK_EQ(G.V(), 13);
     CHECK_EQ(G.E(), 18);
   }
@@ -116,7 +114,7 @@ TEST_SUITE("Graph") {
     G.insert(8, 9);
     G.insert(9, 5);
 
-    REQUIRE_EQ(G.adjMatrix.size(), 9);
+    REQUIRE_EQ(G.V(), 9);
 
     auto SCCs = algo::Tarjan<std::uint16_t>(G.adjMatrix).execute();