diff --git a/src/Attribute/AttributeBagNamespaced.php b/src/Attribute/AttributeBagNamespaced.php
index 840b07ee..515acce1 100644
--- a/src/Attribute/AttributeBagNamespaced.php
+++ b/src/Attribute/AttributeBagNamespaced.php
@@ -93,11 +93,11 @@ public function removeAttribute($name)
     public function getAttributes()
     {
         $attributes = array();
-        $len = strlen($this->prefix);
+        $len = \strlen($this->prefix);
 
         foreach ($this->bag->getAttributes() as $name => $value) {
-            if (strpos($name, $this->prefix) === 0) {
-                $attributes[substr($name, $len)] = $value;
+            if (\strpos($name, $this->prefix) === 0) {
+                $attributes[\substr($name, $len)] = $value;
             }
         }
 
diff --git a/src/Graph.php b/src/Graph.php
index 5bb68258..be3fcbea 100644
--- a/src/Graph.php
+++ b/src/Graph.php
@@ -115,14 +115,14 @@ public function createEdgeDirected(Vertex $source, Vertex $target)
     public function createVertices($n)
     {
         $vertices = array();
-        if (is_int($n) && $n >= 0) {
+        if (\is_int($n) && $n >= 0) {
             for ($id = $this->getNextId(), $n += $id; $id < $n; ++$id) {
                 $vertices[$id] = new Vertex($this, $id);
             }
-        } elseif (is_array($n)) {
+        } elseif (\is_array($n)) {
             // array given => check to make sure all given IDs are available (atomic operation)
             foreach ($n as $id) {
-                if (!is_int($id) && !is_string($id)) {
+                if (!\is_int($id) && !\is_string($id)) {
                     throw new InvalidArgumentException('All Vertex IDs have to be of type integer or string');
                 } elseif ($this->vertices->hasVertexId($id)) {
                     throw new OverflowException('Given array of Vertex IDs contains an ID that already exists. Given IDs must be unique');
@@ -159,7 +159,7 @@ private function getNextId()
         }
 
         // auto ID
-        return max(array_keys($this->verticesStorage))+1;
+        return \max(\array_keys($this->verticesStorage))+1;
     }
 
     /**
@@ -267,22 +267,22 @@ public function __clone()
 
         $map = array();
         foreach ($vertices as $originalVertex) {
-            assert($originalVertex instanceof Vertex);
+            \assert($originalVertex instanceof Vertex);
 
             $vertex = new Vertex($this, $originalVertex->getId());
             $vertex->getAttributeBag()->setAttributes($originalVertex->getAttributeBag()->getAttributes());
 
             // create map with old vertex hash to new vertex object
-            $map[spl_object_hash($originalVertex)] = $vertex;
+            $map[\spl_object_hash($originalVertex)] = $vertex;
         }
 
         foreach ($edges as $originalEdge) {
-            assert($originalEdge instanceof Edge);
+            \assert($originalEdge instanceof Edge);
 
             // use map to match old vertex hashes to new vertex objects
             $vertices = $originalEdge->getVertices()->getVector();
-            $v1 = $map[spl_object_hash($vertices[0])];
-            $v2 = $map[spl_object_hash($vertices[1])];
+            $v1 = $map[\spl_object_hash($vertices[0])];
+            $v2 = $map[\spl_object_hash($vertices[1])];
 
             // recreate edge and assign attributes
             if ($originalEdge instanceof EdgeUndirected) {
diff --git a/src/Set/Edges.php b/src/Set/Edges.php
index 37ba8dc5..acd32340 100644
--- a/src/Set/Edges.php
+++ b/src/Set/Edges.php
@@ -76,7 +76,7 @@ public function __construct(array $edges = array())
      */
     public function getIndexEdge(Edge $edge)
     {
-        $id = array_search($edge, $this->edges, true);
+        $id = \array_search($edge, $this->edges, true);
         if ($id === false) {
             throw new OutOfBoundsException('Given edge does NOT exist');
         }
@@ -99,9 +99,9 @@ public function getEdgeFirst()
         if (!$this->edges) {
             throw new UnderflowException('Does not contain any edges');
         }
-        reset($this->edges);
+        \reset($this->edges);
 
-        return current($this->edges);
+        return \current($this->edges);
     }
 
     /**
@@ -115,9 +115,9 @@ public function getEdgeLast()
         if (!$this->edges) {
             throw new UnderflowException('Does not contain any edges');
         }
-        end($this->edges);
+        \end($this->edges);
 
-        return current($this->edges);
+        return \current($this->edges);
     }
 
     /**
@@ -133,7 +133,7 @@ public function getEdgeRandom()
             throw new UnderflowException('Does not contain any edges');
         }
 
-        return $this->edges[array_rand($this->edges)];
+        return $this->edges[\array_rand($this->edges)];
     }
 
     /**
@@ -196,7 +196,7 @@ public function hasEdgeMatch($callbackCheck)
      */
     public function getEdgesMatch($callbackCheck)
     {
-        return new static(array_filter($this->edges, $callbackCheck));
+        return new static(\array_filter($this->edges, $callbackCheck));
     }
 
     /**
@@ -213,7 +213,7 @@ public function getEdgesOrder($orderBy, $desc = false)
         $callback = $this->getCallback($orderBy);
         $array    = $this->edges;
 
-        uasort($array, function (Edge $va, Edge $vb) use ($callback, $desc) {
+        \uasort($array, function (Edge $va, Edge $vb) use ($callback, $desc) {
             $ra = $callback($desc ? $vb : $va);
             $rb = $callback($desc ? $va : $vb);
 
@@ -242,8 +242,8 @@ public function getEdgesOrder($orderBy, $desc = false)
     public function getEdgesShuffled()
     {
         // shuffle the edge positions
-        $keys = array_keys($this->edges);
-        shuffle($keys);
+        $keys = \array_keys($this->edges);
+        \shuffle($keys);
 
         // re-order according to shuffled edge positions
         $edges = array();
@@ -305,7 +305,7 @@ public function getEdgesDistinct()
         $edges = array();
         foreach ($this->edges as $edge) {
             // filter duplicate edges
-            if (!in_array($edge, $edges, true)) {
+            if (!\in_array($edge, $edges, true)) {
                 $edges []= $edge;
             }
         }
@@ -333,7 +333,7 @@ public function getEdgesIntersection($otherEdges)
 
         $edges = array();
         foreach ($this->edges as $eid => $edge) {
-            $i = array_search($edge, $otherArray, true);
+            $i = \array_search($edge, $otherArray, true);
 
             if ($i !== false) {
                 // remove from other array in order to check for duplicate matches
@@ -353,7 +353,7 @@ public function getEdgesIntersection($otherEdges)
      */
     public function getVector()
     {
-        return array_values($this->edges);
+        return \array_values($this->edges);
     }
 
     /**
@@ -364,7 +364,7 @@ public function getVector()
      */
     public function count()
     {
-        return count($this->edges);
+        return \count($this->edges);
     }
 
     /**
@@ -431,10 +431,10 @@ private function getEdgeMatchOrNull($callbackCheck)
      */
     private function getCallback($callback)
     {
-        if (is_callable($callback)) {
-            if (is_array($callback)) {
+        if (\is_callable($callback)) {
+            if (\is_array($callback)) {
                 $callback = function (Edge $edge) use ($callback) {
-                    return call_user_func($callback, $edge);
+                    return \call_user_func($callback, $edge);
                 };
             }
             return $callback;
diff --git a/src/Set/Vertices.php b/src/Set/Vertices.php
index bc40c9de..4692a126 100644
--- a/src/Set/Vertices.php
+++ b/src/Set/Vertices.php
@@ -109,7 +109,7 @@ public function hasVertexId($id)
      */
     public function getIndexVertex(Vertex $vertex)
     {
-        $id = array_search($vertex, $this->vertices, true);
+        $id = \array_search($vertex, $this->vertices, true);
         if ($id === false) {
             throw new OutOfBoundsException('Given vertex does NOT exist');
         }
@@ -132,9 +132,9 @@ public function getVertexFirst()
         if (!$this->vertices) {
             throw new UnderflowException('Does not contain any vertices');
         }
-        reset($this->vertices);
+        \reset($this->vertices);
 
-        return current($this->vertices);
+        return \current($this->vertices);
     }
 
     /**
@@ -148,9 +148,9 @@ public function getVertexLast()
         if (!$this->vertices) {
             throw new UnderflowException('Does not contain any vertices');
         }
-        end($this->vertices);
+        \end($this->vertices);
 
-        return current($this->vertices);
+        return \current($this->vertices);
     }
 
     /**
@@ -166,7 +166,7 @@ public function getVertexRandom()
             throw new UnderflowException('Does not contain any vertices');
         }
 
-        return $this->vertices[array_rand($this->vertices)];
+        return $this->vertices[\array_rand($this->vertices)];
     }
 
     /**
@@ -215,7 +215,7 @@ public function hasVertexMatch($callbackCheck)
      */
     public function getVerticesMatch($callbackCheck)
     {
-        return new static(array_filter($this->vertices, $callbackCheck));
+        return new static(\array_filter($this->vertices, $callbackCheck));
     }
 
     /**
@@ -234,7 +234,7 @@ public function getVerticesOrder($orderBy, $desc = false)
         $callback = $this->getCallback($orderBy);
         $array    = $this->vertices;
 
-        uasort($array, function (Vertex $va, Vertex $vb) use ($callback, $desc) {
+        \uasort($array, function (Vertex $va, Vertex $vb) use ($callback, $desc) {
             $ra = $callback($desc ? $vb : $va);
             $rb = $callback($desc ? $va : $vb);
 
@@ -263,8 +263,8 @@ public function getVerticesOrder($orderBy, $desc = false)
     public function getVerticesShuffled()
     {
         // shuffle the vertex positions
-        $keys = array_keys($this->vertices);
-        shuffle($keys);
+        $keys = \array_keys($this->vertices);
+        \shuffle($keys);
 
         // re-order according to shuffled vertex positions
         $vertices = array();
@@ -295,7 +295,7 @@ public function getVerticesIntersection($otherVertices)
 
         $vertices = array();
         foreach ($this->vertices as $vid => $vertex) {
-            $i = array_search($vertex, $otherArray, true);
+            $i = \array_search($vertex, $otherArray, true);
 
             if ($i !== false) {
                 // remove from other array in order to check for duplicate matches
@@ -397,7 +397,7 @@ public function getIds()
      */
     public function getVector()
     {
-        return array_values($this->vertices);
+        return \array_values($this->vertices);
     }
 
     /**
@@ -408,7 +408,7 @@ public function getVector()
      */
     public function count()
     {
-        return count($this->vertices);
+        return \count($this->vertices);
     }
 
     /**
@@ -432,7 +432,7 @@ public function isEmpty()
      */
     public function hasDuplicates()
     {
-        return (count($this->vertices) !== count($this->getMap()));
+        return (\count($this->vertices) !== \count($this->getMap()));
     }
 
     /**
@@ -493,10 +493,10 @@ private function getVertexMatchOrNull($callbackCheck)
      */
     private function getCallback($callback)
     {
-        if (is_callable($callback)) {
-            if (is_array($callback)) {
+        if (\is_callable($callback)) {
+            if (\is_array($callback)) {
                 $callback = function (Vertex $vertex) use ($callback) {
-                    return call_user_func($callback, $vertex);
+                    return \call_user_func($callback, $vertex);
                 };
             }
             return $callback;
diff --git a/src/Set/VerticesMap.php b/src/Set/VerticesMap.php
index e70e6c41..f894ac64 100644
--- a/src/Set/VerticesMap.php
+++ b/src/Set/VerticesMap.php
@@ -39,7 +39,7 @@ public function getVerticesDistinct()
 
     public function getIds()
     {
-        return array_keys($this->vertices);
+        return \array_keys($this->vertices);
     }
 
     public function getIndexVertex(Vertex $vertex)
diff --git a/src/Vertex.php b/src/Vertex.php
index 3298f99d..bd24d304 100644
--- a/src/Vertex.php
+++ b/src/Vertex.php
@@ -35,7 +35,7 @@ class Vertex implements EdgesAggregate, AttributeAware
      */
     public function __construct(Graph $graph, $id)
     {
-        if (!is_int($id) && !is_string($id)) {
+        if (!\is_int($id) && !\is_string($id)) {
             throw new InvalidArgumentException('Vertex ID has to be of type integer or string');
         }
 
@@ -89,7 +89,7 @@ public function addEdge(Edge $edge)
      */
     public function removeEdge(Edge $edge)
     {
-        $id = array_search($edge, $this->edges, true);
+        $id = \array_search($edge, $this->edges, true);
         if ($id === false) {
             throw new InvalidArgumentException('Given edge does NOT exist');
         }
diff --git a/src/Walk.php b/src/Walk.php
index 4a21746d..f79ff9fc 100644
--- a/src/Walk.php
+++ b/src/Walk.php
@@ -116,10 +116,10 @@ public static function factoryCycleFromPredecessorMap(array $predecessors, Verte
         } while (!isset($vertices[$vid]));
 
         // reverse cycle, because cycle is actually built in opposite direction due to checking predecessors
-        $vertices = array_reverse($vertices, true);
+        $vertices = \array_reverse($vertices, true);
 
         // additional edge from last vertex to first vertex
-        $vertices[] = reset($vertices);
+        $vertices[] = \reset($vertices);
 
         return self::factoryCycleFromVertices($vertices, $orderBy, $desc);
     }
@@ -245,7 +245,7 @@ public function getAlternatingSequence()
         $vertices = $this->vertices->getVector();
 
         $ret = array();
-        for ($i = 0, $l = count($this->edges); $i < $l; ++$i) {
+        for ($i = 0, $l = \count($this->edges); $i < $l; ++$i) {
             $ret []= $vertices[$i];
             $ret []= $edges[$i];
         }
@@ -275,7 +275,7 @@ public function isValid()
         $edges = $this->getGraph()->getEdges()->getVector();
         // check source graph contains all edges
         foreach ($this->edges as $edge) {
-            if (!in_array($edge, $edges, true)) {
+            if (!\in_array($edge, $edges, true)) {
                 return false;
             }
         }