public function createVertices($n)
    {
        $vertices = array();
        if (is_int($n) && $n >= 0) {
            for ($id = $this->getNextId(), $n += $id; $id < $n; ++$id) {
                $vertices[$id] = new Vertex($this, $id);
            }
        } elseif (is_array($n)) {
            // array given => check to make sure all given IDs are available (atomic operation)
            foreach ($n as $id) {
                if (!is_int($id) && !is_string($id)) {
                    throw new InvalidArgumentException('All Vertex IDs have to be of type integer or string');
                } elseif ($this->vertices->hasVertexId($id)) {
                    throw new OverflowException('Given array of Vertex IDs contains an ID that already exists. Given IDs must be unique');
                } elseif (isset($vertices[$id])) {
                    throw new InvalidArgumentException('Given array of Vertex IDs contain duplicate IDs. Given IDs must be unique');
                }

                // temporary marker to check for duplicate IDs in the array
                $vertices[$id] = false;
            }

            // actually create all requested vertices
            foreach ($n as $id) {
                $vertices[$id] = new Vertex($this, $id);
            }
        } else {
            throw new InvalidArgumentException('Invalid number of vertices given. Must be non-negative integer or an array of Vertex IDs');
        }

        return new Vertices($vertices);
    }