diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6bd3732a..cc068d4b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -75,6 +75,20 @@ you spot any mistakes.
     accordingly.
     ([#72](https://github.com/clue/graph/issues/72))
 
+*   BC break: Remove all occurances of `getNumberOfVertices()` and
+    `getNumberOfEdges()` ([#75](https://github.com/clue/graph/issues/75) and
+    [#48](https://github.com/clue/graph/issues/48)):
+
+    | Old name | New name |
+    |---|---|
+    | `$set->getNumberOfVertices()` | `count($set->getVertices())` |
+    | `$set->getNumberOfEdges()` | `count($set->getEdges())` |
+    
+*   BC break: Replace base `Set` class with `Set\DualAggregate` interface. This
+    is unlikely to affect you, but might potentially break your custom
+    inheritance or polymorphism for algorithms.
+    ([#75](https://github.com/clue/graph/issues/75))
+
 *   Feature: Add `Algorithm\ShortestPath\Base::hasVertex(Vertex $vertex)` to check whether
     a path to the given Vertex exists ([#62](https://github.com/clue/graph/issues/62)).
 
diff --git a/lib/Fhaculty/Graph/Algorithm/BaseSet.php b/lib/Fhaculty/Graph/Algorithm/BaseDual.php
similarity index 76%
rename from lib/Fhaculty/Graph/Algorithm/BaseSet.php
rename to lib/Fhaculty/Graph/Algorithm/BaseDual.php
index c12cdec7..f657ff3d 100644
--- a/lib/Fhaculty/Graph/Algorithm/BaseSet.php
+++ b/lib/Fhaculty/Graph/Algorithm/BaseDual.php
@@ -3,7 +3,7 @@
 namespace Fhaculty\Graph\Algorithm;
 
 use Fhaculty\Graph\Algorithm\Base;
-use Fhaculty\Graph\Set;
+use Fhaculty\Graph\Set\DualAggregate;
 use Fhaculty\Graph\Graph;
 use Fhaculty\Graph\Walk;
 
@@ -12,12 +12,12 @@
  *
  * @see Set
  */
-abstract class BaseSet extends Base
+abstract class BaseDual extends Base
 {
     /**
      * Set to operate on
      *
-     * @var Set
+     * @var DualAggregate
      */
     protected $set;
 
@@ -26,7 +26,7 @@ abstract class BaseSet extends Base
      *
      * @param Graph|Walk|Set $graphOrWalk either the Graph or Walk to operate on (or the common base class Set)
      */
-    public function __construct(Set $graphOrWalk)
+    public function __construct(DualAggregate $graphOrWalk)
     {
         $this->set = $graphOrWalk;
     }
diff --git a/lib/Fhaculty/Graph/Algorithm/ConnectedComponents.php b/lib/Fhaculty/Graph/Algorithm/ConnectedComponents.php
index cfaf0494..3da187b5 100644
--- a/lib/Fhaculty/Graph/Algorithm/ConnectedComponents.php
+++ b/lib/Fhaculty/Graph/Algorithm/ConnectedComponents.php
@@ -65,7 +65,6 @@ private function createSearch(Vertex $vertex)
      * connected here.
      *
      * @return boolean
-     * @uses AlgorithmSearchBreadthFirst::getNumberOfVertices()
      * @see self::getNumberOfComponents()
      */
     public function isSingle()
@@ -79,7 +78,7 @@ public function isSingle()
         }
         $alg = $this->createSearch($vertex);
 
-        return ($this->graph->getNumberOfVertices() === $alg->getNumberOfVertices());
+        return (count($this->graph->getVertices()) === count($alg->getVertices()));
     }
 
     /**
diff --git a/lib/Fhaculty/Graph/Algorithm/Directed.php b/lib/Fhaculty/Graph/Algorithm/Directed.php
index b984c97d..e8ee9d24 100644
--- a/lib/Fhaculty/Graph/Algorithm/Directed.php
+++ b/lib/Fhaculty/Graph/Algorithm/Directed.php
@@ -11,7 +11,7 @@
  * @link http://en.wikipedia.org/wiki/Glossary_of_graph_theory#Direction
  * @link http://en.wikipedia.org/wiki/Digraph_%28mathematics%29
  */
-class Directed extends BaseSet
+class Directed extends BaseDual
 {
     /**
      * checks whether the graph has any directed edges (aka digraph)
diff --git a/lib/Fhaculty/Graph/Algorithm/Flow.php b/lib/Fhaculty/Graph/Algorithm/Flow.php
index 6ae06843..7130019b 100644
--- a/lib/Fhaculty/Graph/Algorithm/Flow.php
+++ b/lib/Fhaculty/Graph/Algorithm/Flow.php
@@ -18,7 +18,7 @@
  * @link http://en.wikipedia.org/wiki/Flow_network
  * @see Algorithm\Balance
  */
-class Flow extends BaseSet
+class Flow extends BaseDual
 {
     /**
      * check if this graph has any flow set (any edge has a non-NULL flow)
diff --git a/lib/Fhaculty/Graph/Algorithm/Loop.php b/lib/Fhaculty/Graph/Algorithm/Loop.php
index 4511edbb..d52bbdd4 100644
--- a/lib/Fhaculty/Graph/Algorithm/Loop.php
+++ b/lib/Fhaculty/Graph/Algorithm/Loop.php
@@ -2,7 +2,7 @@
 
 namespace Fhaculty\Graph\Algorithm;
 
-use Fhaculty\Graph\Algorithm\BaseSet;
+use Fhaculty\Graph\Algorithm\BaseDual;
 use Fhaculty\Graph\Edge\Base as Edge;
 use Fhaculty\Graph\Vertex;
 
@@ -14,7 +14,7 @@
  *
  * @link http://en.wikipedia.org/wiki/Loop_%28graph_theory%29
  */
-class Loop extends BaseSet
+class Loop extends BaseDual
 {
     /**
      * checks whether this graph has any loops (edges from vertex to itself)
diff --git a/lib/Fhaculty/Graph/Algorithm/MinimumCostFlow/SuccessiveShortestPath.php b/lib/Fhaculty/Graph/Algorithm/MinimumCostFlow/SuccessiveShortestPath.php
index b9719d3e..66bc4d55 100644
--- a/lib/Fhaculty/Graph/Algorithm/MinimumCostFlow/SuccessiveShortestPath.php
+++ b/lib/Fhaculty/Graph/Algorithm/MinimumCostFlow/SuccessiveShortestPath.php
@@ -124,13 +124,12 @@ public function createGraph()
      * @param  Graph     $graph
      * @return boolean
      * @throws Exception if given graph is not a clone of the original graph (each vertex has to be present in both graphs)
-     * @uses Graph::getNumberOfVertices()
      * @uses Graph::getBalanace()
      * @uses Graph::getVertex()
      */
     private function isBalanceReached(Graph $graph)
     {
-        if ($graph->getNumberOfVertices() !== $this->graph->getNumberOfVertices()) {
+        if (count($graph->getVertices()) !== count($this->graph->getVertices())) {
             throw new DomainException('Given graph does not appear to be a clone of input graph');
         }
         foreach ($this->graph->getVertices()->getMap() as $vid => $vertex) {
diff --git a/lib/Fhaculty/Graph/Algorithm/MinimumSpanningTree/Kruskal.php b/lib/Fhaculty/Graph/Algorithm/MinimumSpanningTree/Kruskal.php
index 26095cc7..6c29a90e 100644
--- a/lib/Fhaculty/Graph/Algorithm/MinimumSpanningTree/Kruskal.php
+++ b/lib/Fhaculty/Graph/Algorithm/MinimumSpanningTree/Kruskal.php
@@ -125,7 +125,7 @@ public function getEdges()
 
         // definition of spanning tree: number of edges = number of vertices - 1
         // above algorithm does not check isolated edges or may otherwise return multiple connected components => force check
-        if (count($returnEdges) !== ($this->graph->getNumberOfVertices() - 1)) {
+        if (count($returnEdges) !== (count($this->graph->getVertices()) - 1)) {
             throw new UnexpectedValueException('Graph is not connected');
         }
 
diff --git a/lib/Fhaculty/Graph/Algorithm/MinimumSpanningTree/Prim.php b/lib/Fhaculty/Graph/Algorithm/MinimumSpanningTree/Prim.php
index adaa1fc5..51518462 100644
--- a/lib/Fhaculty/Graph/Algorithm/MinimumSpanningTree/Prim.php
+++ b/lib/Fhaculty/Graph/Algorithm/MinimumSpanningTree/Prim.php
@@ -35,7 +35,7 @@ public function getEdges()
         $returnEdges = array();
 
         // iterate n-1 times (per definition, resulting MST MUST have n-1 edges)
-        for ($i = 0, $n = $this->startVertex->getGraph()->getNumberOfVertices() - 1; $i < $n; ++$i) {
+        for ($i = 0, $n = count($this->startVertex->getGraph()->getVertices()) - 1; $i < $n; ++$i) {
             $markInserted[$vertexCurrent->getId()] = true;
 
             // get unvisited vertex of the edge and add edges from new vertex
diff --git a/lib/Fhaculty/Graph/Algorithm/Property/GraphProperty.php b/lib/Fhaculty/Graph/Algorithm/Property/GraphProperty.php
index 88995529..90c21575 100644
--- a/lib/Fhaculty/Graph/Algorithm/Property/GraphProperty.php
+++ b/lib/Fhaculty/Graph/Algorithm/Property/GraphProperty.php
@@ -46,6 +46,6 @@ public function isNull()
      */
     public function isTrivial()
     {
-        return ($this->graph->getEdges()->isEmpty() && $this->graph->getNumberOfVertices() === 1);
+        return ($this->graph->getEdges()->isEmpty() && count($this->graph->getVertices()) === 1);
     }
 }
diff --git a/lib/Fhaculty/Graph/Algorithm/Property/WalkProperty.php b/lib/Fhaculty/Graph/Algorithm/Property/WalkProperty.php
index fd31b44e..427ecf10 100644
--- a/lib/Fhaculty/Graph/Algorithm/Property/WalkProperty.php
+++ b/lib/Fhaculty/Graph/Algorithm/Property/WalkProperty.php
@@ -162,7 +162,7 @@ public function hasCycle()
      */
     public function isLoop()
     {
-        return ($this->walk->getNumberOfEdges() === 1 && $this->isCycle());
+        return (count($this->walk->getEdges()) === 1 && $this->isCycle());
     }
 
     /**
@@ -214,7 +214,7 @@ public function hasLoop()
     public function isDigon()
     {
         // exactly 2 edges
-        return ($this->walk->getNumberOfEdges() === 2 &&
+        return (count($this->walk->getEdges()) === 2 &&
                 // no duplicate edges
                 !$this->hasArrayDuplicates($this->walk->getEdges()->getVector()) &&
                 // exactly two distinct vertices
@@ -238,7 +238,7 @@ public function isDigon()
     public function isTriangle()
     {
         // exactly 3 (implicitly distinct) edges
-        return ($this->walk->getNumberOfEdges() === 3 &&
+        return (count($this->walk->getEdges()) === 3 &&
                 // exactly three distinct vertices
                 count($this->walk->getVertices()->getVerticesDistinct()) === 3 &&
                 // this is actually a cycle
diff --git a/lib/Fhaculty/Graph/Algorithm/Search/Base.php b/lib/Fhaculty/Graph/Algorithm/Search/Base.php
index a7c37856..a47bf921 100644
--- a/lib/Fhaculty/Graph/Algorithm/Search/Base.php
+++ b/lib/Fhaculty/Graph/Algorithm/Search/Base.php
@@ -47,17 +47,6 @@ protected function getVerticesAdjacent(Vertex $vertex)
         }
     }
 
-    /**
-     * get total number of vertices the start vertex is connected to
-     *
-     * @return int
-     * @uses AlgorithmSearch::getVertices()
-     */
-    public function getNumberOfVertices()
-    {
-        return count($this->getVertices());
-    }
-
     /**
      * get set of all Vertices that can be reached from start vertex
      *
diff --git a/lib/Fhaculty/Graph/Algorithm/ShortestPath/Dijkstra.php b/lib/Fhaculty/Graph/Algorithm/ShortestPath/Dijkstra.php
index 35759d23..3600d7b3 100644
--- a/lib/Fhaculty/Graph/Algorithm/ShortestPath/Dijkstra.php
+++ b/lib/Fhaculty/Graph/Algorithm/ShortestPath/Dijkstra.php
@@ -46,7 +46,7 @@ public function getEdges()
         $isFirst = true;
 
         // Repeat until all vertices have been marked
-        $totalCountOfVertices = $this->vertex->getGraph()->getNumberOfVertices();
+        $totalCountOfVertices = count($this->vertex->getGraph()->getVertices());
         for ($i = 0; $i < $totalCountOfVertices; ++$i) {
             $currentVertex = NULL;
             $currentVertexId = NULL;
diff --git a/lib/Fhaculty/Graph/Algorithm/ShortestPath/MooreBellmanFord.php b/lib/Fhaculty/Graph/Algorithm/ShortestPath/MooreBellmanFord.php
index bd9b2051..e954230a 100644
--- a/lib/Fhaculty/Graph/Algorithm/ShortestPath/MooreBellmanFord.php
+++ b/lib/Fhaculty/Graph/Algorithm/ShortestPath/MooreBellmanFord.php
@@ -79,7 +79,7 @@ public function getEdges()
         // the usal algorithm says we repeat (n-1) times.
         // but because we also want to check for loop edges on the start vertex,
         // we have to add an additional step:
-        $numSteps = $this->vertex->getGraph()->getNumberOfVertices();
+        $numSteps = count($this->vertex->getGraph()->getVertices());
         $edges = $this->vertex->getGraph()->getEdges();
         $changed = true;
 
diff --git a/lib/Fhaculty/Graph/Algorithm/TravelingSalesmanProblem/Bruteforce.php b/lib/Fhaculty/Graph/Algorithm/TravelingSalesmanProblem/Bruteforce.php
index e97acfee..00b02f55 100644
--- a/lib/Fhaculty/Graph/Algorithm/TravelingSalesmanProblem/Bruteforce.php
+++ b/lib/Fhaculty/Graph/Algorithm/TravelingSalesmanProblem/Bruteforce.php
@@ -108,7 +108,7 @@ protected function getGraph()
      */
     public function getEdges()
     {
-        $this->numEdges = $this->graph->getNumberOfVertices();
+        $this->numEdges = count($this->graph->getVertices());
         if ($this->numEdges < 3) {
             throw new UnderflowException('Needs at least 3 vertices');
         }
diff --git a/lib/Fhaculty/Graph/Algorithm/TravelingSalesmanProblem/NearestNeighbor.php b/lib/Fhaculty/Graph/Algorithm/TravelingSalesmanProblem/NearestNeighbor.php
index fc55f5b2..e198045a 100644
--- a/lib/Fhaculty/Graph/Algorithm/TravelingSalesmanProblem/NearestNeighbor.php
+++ b/lib/Fhaculty/Graph/Algorithm/TravelingSalesmanProblem/NearestNeighbor.php
@@ -40,7 +40,7 @@ public function getEdges()
     {
         $returnEdges = array();
 
-        $n = $this->vertex->getGraph()->getNumberOfVertices();
+        $n = count($this->vertex->getGraph()->getVertices());
 
         $vertex = $this->vertex;
         $visitedVertices = array($vertex->getId() => true);
diff --git a/lib/Fhaculty/Graph/Algorithm/Tree/BaseDirected.php b/lib/Fhaculty/Graph/Algorithm/Tree/BaseDirected.php
index e67e99c8..ef557793 100644
--- a/lib/Fhaculty/Graph/Algorithm/Tree/BaseDirected.php
+++ b/lib/Fhaculty/Graph/Algorithm/Tree/BaseDirected.php
@@ -96,7 +96,7 @@ public function isTree()
         }
 
         // check number of vertices reachable from root should match total number of vertices
-        return ($num === $this->graph->getNumberOfVertices());
+        return ($num === count($this->graph->getVertices()));
     }
 
     /**
diff --git a/lib/Fhaculty/Graph/Algorithm/Tree/Undirected.php b/lib/Fhaculty/Graph/Algorithm/Tree/Undirected.php
index 8f55d4af..01157d9b 100644
--- a/lib/Fhaculty/Graph/Algorithm/Tree/Undirected.php
+++ b/lib/Fhaculty/Graph/Algorithm/Tree/Undirected.php
@@ -70,7 +70,7 @@ public function isTree()
             return false;
         }
 
-        return (count($vertices) === $this->graph->getNumberOfVertices());
+        return (count($vertices) === count($this->graph->getVertices()));
     }
 
     /**
diff --git a/lib/Fhaculty/Graph/Algorithm/Weight.php b/lib/Fhaculty/Graph/Algorithm/Weight.php
index e8e548bd..38445635 100644
--- a/lib/Fhaculty/Graph/Algorithm/Weight.php
+++ b/lib/Fhaculty/Graph/Algorithm/Weight.php
@@ -15,7 +15,7 @@
  *
  * @link http://en.wikipedia.org/wiki/Glossary_of_graph_theory#Weighted_graphs_and_networks
  */
-class Weight extends BaseSet
+class Weight extends BaseDual
 {
     /**
      * checks whether this graph has any weighted edges
diff --git a/lib/Fhaculty/Graph/Graph.php b/lib/Fhaculty/Graph/Graph.php
index b18cd6d1..12392d65 100644
--- a/lib/Fhaculty/Graph/Graph.php
+++ b/lib/Fhaculty/Graph/Graph.php
@@ -20,8 +20,9 @@
 use Fhaculty\Graph\Set\Vertices;
 use Fhaculty\Graph\Set\VerticesMap;
 use Fhaculty\Graph\Set\Edges;
+use Fhaculty\Graph\Set\DualAggregate;
 
-class Graph extends Set
+class Graph implements DualAggregate
 {
     /**
      * @var ExporterInterface|null
diff --git a/lib/Fhaculty/Graph/Set.php b/lib/Fhaculty/Graph/Set.php
deleted file mode 100644
index 3f621efb..00000000
--- a/lib/Fhaculty/Graph/Set.php
+++ /dev/null
@@ -1,52 +0,0 @@
-<?php
-
-namespace Fhaculty\Graph;
-
-use Fhaculty\Graph\Edge\Base as Edge;
-use Fhaculty\Graph\Set\Edges;
-use Fhaculty\Graph\Set\EdgesAggregate;
-use Fhaculty\Graph\Set\Vertices;
-use Fhaculty\Graph\Set\VerticesAggregate;
-
-/**
- *
- * @author clue
- * @link http://en.wikipedia.org/wiki/Path_%28graph_theory%29
- * @link http://en.wikipedia.org/wiki/Glossary_of_graph_theory#Walks
- */
-abstract class Set implements VerticesAggregate, EdgesAggregate
-{
-    /**
-     * returns a set of ALL Edges in this graph
-     *
-     * @return Edges
-     */
-    // abstract public function getEdges();
-
-    /**
-     * returns a set of all Vertices
-     *
-     * @return Vertices
-     */
-    // abstract public function getVertices();
-
-    /**
-     * return number of vertices (aka. size of graph, |V| or just 'n')
-     *
-     * @return int
-     */
-    public function getNumberOfVertices()
-    {
-        return count($this->getVertices());
-    }
-
-    /**
-     * return number of edges
-     *
-     * @return int
-     */
-    public function getNumberOfEdges()
-    {
-        return count($this->getEdges());
-    }
-}
diff --git a/lib/Fhaculty/Graph/Set/DualAggregate.php b/lib/Fhaculty/Graph/Set/DualAggregate.php
new file mode 100644
index 00000000..6bd370c3
--- /dev/null
+++ b/lib/Fhaculty/Graph/Set/DualAggregate.php
@@ -0,0 +1,30 @@
+<?php
+
+namespace Fhaculty\Graph\Set;
+
+use Fhaculty\Graph\Set\VerticesAggregate;
+use Fhaculty\Graph\Set\EdgesAggregate;
+
+/**
+ * DualAggregate provides access to both its Vertices and its Edges
+ *
+ * This is the simple base interface for any Graph-like structure / data type
+ * which contains a Set of Edges and a Set of Vertices, such as the Graph class
+ * itself and the Walk class.
+ */
+interface DualAggregate extends VerticesAggregate, EdgesAggregate
+{
+    /**
+     * returns a set of ALL Edges in this graph
+     *
+     * @return Edges
+     */
+    // abstract public function getEdges();
+
+    /**
+     * returns a set of all Vertices
+     *
+     * @return Vertices
+     */
+    // abstract public function getVertices();
+}
diff --git a/lib/Fhaculty/Graph/Walk.php b/lib/Fhaculty/Graph/Walk.php
index 0b192801..4beaed6c 100644
--- a/lib/Fhaculty/Graph/Walk.php
+++ b/lib/Fhaculty/Graph/Walk.php
@@ -3,12 +3,11 @@
 namespace Fhaculty\Graph;
 
 use Fhaculty\Graph\Set\Edges;
-use Fhaculty\Graph\Set\EdgesAggregate;
 use Fhaculty\Graph\Set\Vertices;
-use Fhaculty\Graph\Set\VerticesAggregate;
 use Fhaculty\Graph\Edge\Base as Edge;
 use Fhaculty\Graph\Exception\UnderflowException;
 use Fhaculty\Graph\Exception\InvalidArgumentException;
+use Fhaculty\Graph\Set\DualAggregate;
 
 /**
  * Base Walk class
@@ -20,7 +19,7 @@
  * @link http://en.wikipedia.org/wiki/Glossary_of_graph_theory#Walks
  * @see Fhaculty\Graph\Algorithm\Property\WalkProperty for checking special cases, such as cycles, loops, closed trails, etc.
  */
-class Walk extends Set implements VerticesAggregate, EdgesAggregate
+class Walk implements DualAggregate
 {
     /**
      * construct new walk from given start vertex and given array of edges
diff --git a/tests/Fhaculty/Graph/Algorithm/Property/WalkPropertyTest.php b/tests/Fhaculty/Graph/Algorithm/Property/WalkPropertyTest.php
index 79c14e46..8fd4313b 100644
--- a/tests/Fhaculty/Graph/Algorithm/Property/WalkPropertyTest.php
+++ b/tests/Fhaculty/Graph/Algorithm/Property/WalkPropertyTest.php
@@ -14,8 +14,8 @@ public function testTrivialGraph()
 
         $walk = Walk::factoryFromEdges(array(), $v1);
 
-        $this->assertEquals(1, $walk->getNumberOfVertices());
-        $this->assertEquals(0, $walk->getNumberOfEdges());
+        $this->assertEquals(1, count($walk->getVertices()));
+        $this->assertEquals(0, count($walk->getEdges()));
 
         $alg = new WalkProperty($walk);
 
@@ -67,8 +67,8 @@ public function testCycle()
 
         $walk = Walk::factoryFromEdges(array($e1, $e2), $v1);
 
-        $this->assertEquals(3, $walk->getNumberOfVertices());
-        $this->assertEquals(2, $walk->getNumberOfEdges());
+        $this->assertEquals(3, count($walk->getVertices()));
+        $this->assertEquals(2, count($walk->getEdges()));
 
         $alg = new WalkProperty($walk);
 
@@ -170,8 +170,8 @@ public function testSimplePathWithinGraph()
         // only use "2 -- 2" part
         $walk = Walk::factoryFromEdges(array($e2), $v2);
 
-        $this->assertEquals(2, $walk->getNumberOfVertices());
-        $this->assertEquals(1, $walk->getNumberOfEdges());
+        $this->assertEquals(2, count($walk->getVertices()));
+        $this->assertEquals(1, count($walk->getEdges()));
 
         $alg = new WalkProperty($walk);
 
diff --git a/tests/Fhaculty/Graph/Algorithm/ShortestPath/BaseShortestPathTest.php b/tests/Fhaculty/Graph/Algorithm/ShortestPath/BaseShortestPathTest.php
index 9f85222b..65fa5ee4 100644
--- a/tests/Fhaculty/Graph/Algorithm/ShortestPath/BaseShortestPathTest.php
+++ b/tests/Fhaculty/Graph/Algorithm/ShortestPath/BaseShortestPathTest.php
@@ -79,7 +79,7 @@ public function testGraphCycle()
         $this->assertEquals($expectedWeight, $alg->getDistance($v1));
 
         $walk = $alg->getWalkTo($v1);
-        $this->assertEquals(2, $walk->getNumberOfEdges());
+        $this->assertEquals(2, count($walk->getEdges()));
     }
 
     /**
diff --git a/tests/Fhaculty/Graph/GraphTest.php b/tests/Fhaculty/Graph/GraphTest.php
index d59c7521..ad09d99e 100644
--- a/tests/Fhaculty/Graph/GraphTest.php
+++ b/tests/Fhaculty/Graph/GraphTest.php
@@ -185,7 +185,7 @@ public function testCreateMultigraph()
         $e1 = $v1->createEdge($v2);
         $e2 = $v1->createEdge($v2);
 
-        $this->assertEquals(2, $graph->getNumberOfEdges());
+        $this->assertEquals(2, count($graph->getEdges()));
         $this->assertEquals(2, count($v1->getEdges()));
 
         $this->assertEquals(array(2, 2), $v1->getVerticesEdge()->getIds());
@@ -202,7 +202,7 @@ public function testCreateMixedGraph()
         $v1->createEdge($v2);
         $v2->createEdgeTo($v3);
 
-        $this->assertEquals(2, $graph->getNumberOfEdges());
+        $this->assertEquals(2, count($graph->getEdges()));
 
         $this->assertEquals(2, count($v2->getEdges()));
         $this->assertEquals(2, count($v2->getEdgesOut()));
@@ -219,7 +219,7 @@ public function testCreateVerticesNone()
         $this->assertEquals(array(), $graph->createVertices(0)->getVector());
         $this->assertEquals(array(), $graph->createVertices(array())->getVector());
 
-        $this->assertEquals(0, $graph->getNumberOfVertices());
+        $this->assertEquals(0, count($graph->getVertices()));
     }
 
     /**
@@ -274,7 +274,7 @@ public function testCreateVerticesAtomic()
             $this->fail('Should be unable to create vertices because of duplicate IDs');
         }
         catch (OverflowException $ignoreExpected) {
-            $this->assertEquals(10, $graph->getNumberOfVertices());
+            $this->assertEquals(10, count($graph->getVertices()));
         }
 
         try {
@@ -282,7 +282,7 @@ public function testCreateVerticesAtomic()
             $this->fail('Should be unable to create vertices because of duplicate IDs');
         }
         catch (InvalidArgumentException $ignoreExpected) {
-            $this->assertEquals(10, $graph->getNumberOfVertices());
+            $this->assertEquals(10, count($graph->getVertices()));
         }
     }
 
@@ -411,7 +411,7 @@ public function testCreateGraphCloneVertices()
 
         $graphClone = $graph->createGraphCloneVertices(array(1 => $v1, 2 => $v2));
 
-        $this->assertEquals(2, $graphClone->getNumberOfVertices());
-        $this->assertEquals(1, $graphClone->getNumberOfEdges());
+        $this->assertEquals(2, count($graphClone->getVertices()));
+        $this->assertEquals(1, count($graphClone->getEdges()));
     }
 }
diff --git a/tests/Fhaculty/Graph/Loader/CompleteGraphTest.php b/tests/Fhaculty/Graph/Loader/CompleteGraphTest.php
index b3df703b..b39a7f39 100644
--- a/tests/Fhaculty/Graph/Loader/CompleteGraphTest.php
+++ b/tests/Fhaculty/Graph/Loader/CompleteGraphTest.php
@@ -28,8 +28,8 @@ public function testUndirected()
         $loader = new CompleteGraph($n);
         $graph = $loader->createGraph();
 
-        $this->assertEquals($n, $graph->getNumberOfVertices());
-        $this->assertEquals($n*($n-1)/2, $graph->getNumberOfEdges());
+        $this->assertEquals($n, count($graph->getVertices()));
+        $this->assertEquals($n*($n-1)/2, count($graph->getEdges()));
     }
 
     public function testDirected()
@@ -40,8 +40,8 @@ public function testDirected()
         $loader->setEnableDirectedEdges(true);
         $graph = $loader->createGraph();
 
-        $this->assertEquals($n, $graph->getNumberOfVertices());
-        $this->assertEquals($n*($n-1), $graph->getNumberOfEdges()); // n*(n-1) for directed graphs
+        $this->assertEquals($n, count($graph->getVertices()));
+        $this->assertEquals($n*($n-1), count($graph->getEdges())); // n*(n-1) for directed graphs
 
         $alg = new Directed($graph);
         $this->assertTrue($alg->isDirected());
diff --git a/tests/Fhaculty/Graph/WalkTest.php b/tests/Fhaculty/Graph/WalkTest.php
index b8f90745..e0f0239f 100644
--- a/tests/Fhaculty/Graph/WalkTest.php
+++ b/tests/Fhaculty/Graph/WalkTest.php
@@ -26,8 +26,8 @@ public function testWalkPath()
 
         $walk = Walk::factoryFromEdges(array($e1, $e2), $v1);
 
-        $this->assertEquals(3, $walk->getNumberOfVertices());
-        $this->assertEquals(2, $walk->getNumberOfEdges());
+        $this->assertEquals(3, count($walk->getVertices()));
+        $this->assertEquals(2, count($walk->getEdges()));
         $this->assertSame($v1, $walk->getVertexSource());
         $this->assertSame($v3, $walk->getVertexTarget());
         $this->assertSame(array($v1, $e1, $v2, $e2, $v3), $walk->getAlternatingSequence());
@@ -64,8 +64,8 @@ public function testWalkWithinGraph()
         // construct partial walk "1 -- 2"
         $walk = Walk::factoryFromEdges(array($e1), $v1);
 
-        $this->assertEquals(2, $walk->getNumberOfVertices());
-        $this->assertEquals(1, $walk->getNumberOfEdges());
+        $this->assertEquals(2, count($walk->getVertices()));
+        $this->assertEquals(1, count($walk->getEdges()));
         $this->assertSame($v1, $walk->getVertexSource());
         $this->assertSame($v2, $walk->getVertexTarget());
         $this->assertSame(array($v1, $e1, $v2), $walk->getAlternatingSequence());
@@ -79,8 +79,8 @@ public function testWalkWithinGraph()
         // construct same partial walk "1 -- 2"
         $walkVertices = Walk::factoryFromVertices(array($v1, $v2));
 
-        $this->assertEquals(2, $walkVertices->getNumberOfVertices());
-        $this->assertEquals(1, $walkVertices->getNumberOfEdges());
+        $this->assertEquals(2, count($walkVertices->getVertices()));
+        $this->assertEquals(1, count($walkVertices->getEdges()));
 
         $this->assertGraphEquals($graphExpected, $walkVertices->createGraph());
 
@@ -96,8 +96,8 @@ public function testWalkLoop()
 
         $walk = Walk::factoryFromEdges(array($e1), $v1);
 
-        $this->assertEquals(2, $walk->getNumberOfVertices());
-        $this->assertEquals(1, $walk->getNumberOfEdges());
+        $this->assertEquals(2, count($walk->getVertices()));
+        $this->assertEquals(1, count($walk->getEdges()));
         $this->assertSame($v1, $walk->getVertexSource());
         $this->assertSame($v1, $walk->getVertexTarget());
         $this->assertTrue($walk->isValid());
@@ -129,8 +129,8 @@ public function testWalkLoopCycle()
 
         $walk = Walk::factoryCycleFromEdges(array($e1), $v1);
 
-        $this->assertEquals(2, $walk->getNumberOfVertices());
-        $this->assertEquals(1, $walk->getNumberOfEdges());
+        $this->assertEquals(2, count($walk->getVertices()));
+        $this->assertEquals(1, count($walk->getEdges()));
         $this->assertSame($v1, $walk->getVertexSource());
         $this->assertSame($v1, $walk->getVertexTarget());
         $this->assertTrue($walk->isValid());
@@ -148,8 +148,8 @@ public function testWalkCycleFromVerticesAutocomplete()
         // should actually be v1, v2, v1, but cycle factory automatically adds missing vertex + edge
         $walk = Walk::factoryCycleFromVertices(array($v1, $v2));
 
-        $this->assertEquals(3, $walk->getNumberOfVertices());
-        $this->assertEquals(2, $walk->getNumberOfEdges());
+        $this->assertEquals(3, count($walk->getVertices()));
+        $this->assertEquals(2, count($walk->getEdges()));
         $this->assertSame($v1, $walk->getVertexSource());
         $this->assertSame($v1, $walk->getVertexTarget());
         $this->assertTrue($walk->isValid());
diff --git a/tests/bootstrap.php b/tests/bootstrap.php
index 15569fcb..723a8280 100644
--- a/tests/bootstrap.php
+++ b/tests/bootstrap.php
@@ -14,8 +14,8 @@ protected function assertGraphEquals(Graph $expected, Graph $actual)
     {
         $f = function(Graph $graph){
             $ret = get_class($graph);
-            $ret .= PHP_EOL . 'vertices: ' . $graph->getNumberOfVertices();
-            $ret .= PHP_EOL . 'edges: ' . $graph->getNumberOfEdges();
+            $ret .= PHP_EOL . 'vertices: ' . count($graph->getVertices());
+            $ret .= PHP_EOL . 'edges: ' . count($graph->getEdges());
 
             return $ret;
         };