diff --git a/Localization/Localization.php b/Localization/Localization.php
index c4a289a13..fb8d2ba9e 100644
--- a/Localization/Localization.php
+++ b/Localization/Localization.php
@@ -39,7 +39,7 @@ class Localization
      * @var string
      * @since 1.0.0
      */
-    private $country = ISO3166TwoEnum::C_USA;
+    private $country = ISO3166TwoEnum::_USA;
     /**
      * Timezone.
      *
@@ -60,7 +60,7 @@ class Localization
      * @var string
      * @since 1.0.0
      */
-    private $currency = ISO4217Enum::C_USD;
+    private $currency = ISO4217Enum::_USD;
     /**
      * Number format.
      *
diff --git a/Math/Functions/Fibunacci.php b/Math/Functions/Fibunacci.php
index 1ec0b103d..8cdd28cc7 100644
--- a/Math/Functions/Fibunacci.php
+++ b/Math/Functions/Fibunacci.php
@@ -14,7 +14,7 @@
  * @link       http://orange-management.com
  */
 
-namespace phpOMS\Math;
+namespace phpOMS\Math\Functions;
 
 use phpOMS\Math\Number\Numbers;
 
@@ -60,17 +60,15 @@ class Fibunacci
      */
     public static function fibunacci(int $n, int $start = 1) : int
     {
-        if ($n < 2) {
-            return 0;
-        } elseif ($n < 4) {
+        if ($n < 3) {
             return $start;
         }
 
-        $old_1 = 0;
+        $old_1 = $start;
         $old_2 = $start;
         $fib   = 0;
 
-        for ($i = 4; $i < $n; $i++) {
+        for ($i = 2; $i < $n; $i++) {
             $fib   = $old_1 + $old_2;
             $old_1 = $old_2;
             $old_2 = $fib;
diff --git a/Math/Geometry/ConvexHull/MonotoneChain.php b/Math/Geometry/ConvexHull/MonotoneChain.php
index ccf75f508..b802ac0d7 100644
--- a/Math/Geometry/ConvexHull/MonotoneChain.php
+++ b/Math/Geometry/ConvexHull/MonotoneChain.php
@@ -13,7 +13,7 @@
  * @version    1.0.0
  * @link       http://orange-management.com
  */
-namespace phpOMS\Math\Geometry;
+namespace phpOMS\Math\Geometry\ConvexHull;
 
 /**
  * Andrew's monotone chain convex hull algorithm class.
diff --git a/Math/Number/Integer.php b/Math/Number/Integer.php
index e187eb475..9edce5227 100644
--- a/Math/Number/Integer.php
+++ b/Math/Number/Integer.php
@@ -125,10 +125,10 @@ class Integer
      */
     public static function greatestCommonDivisor(int $n, int $m) : int
     {
-        while (true) {
-            if ($n === $m) {
-                return $m;
-            }
+        $n = abs($n);
+        $m = abs($m);
+
+        while ($n !== $m) {
             if ($n > $m) {
                 $n -= $m;
             } else {
@@ -136,7 +136,7 @@ class Integer
             }
         }
 
-        return 1;
+        return $m;
     }
 
     /**
@@ -154,17 +154,18 @@ class Integer
      */
     public static function fermatFactor(int $value, int $limit = 1000000) : array
     {
-        if (($value % 2) !== 0) {
+        if (($value % 2) === 0) {
             throw new \Exception('Only odd integers are allowed');
         }
 
         $a  = (int) ceil(sqrt($value));
-        $b2 = $a * $a - $value;
+        $b2 = (int) ($a * $a - $value);
         $i  = 1;
 
         while (!Numbers::isSquare($b2) && $i < $limit) {
+            $i++;
             $a += 1;
-            $b2 = $a * $a - $value;
+            $b2 = (int) ($a * $a - $value);
         }
 
         return [(int) round($a - sqrt($b2)), (int) round($a + sqrt($b2))];
diff --git a/Math/Number/Numbers.php b/Math/Number/Numbers.php
index 3d06f26b6..06a8a47d0 100644
--- a/Math/Number/Numbers.php
+++ b/Math/Number/Numbers.php
@@ -86,36 +86,7 @@ class Numbers
      */
     public static function isSquare(int $n) : bool
     {
-        $goodMask = 0xC840C04048404040; // 0xC840C04048404040 computed below
-
-        for ($i = 0; $i < 64; ++$i) {
-            $goodMask |= PHP_INT_MIN >> ($i * $i);
-        }
-
-        // This tests if the 6 least significant bits are right.
-        // Moving the to be tested bit to the highest position saves us masking.
-        if ($goodMask << $n >= 0) {
-            return false;
-        }
-
-        $numberOfTrailingZeros = self::countTrailingZeros($n);
-        // Each square ends with an even number of zeros.
-        if (($numberOfTrailingZeros & 1) !== 0) {
-            return false;
-        }
-
-        $n >>= $numberOfTrailingZeros;
-        // Now x is either 0 or odd.
-        // In binary each odd square ends with 001.
-        // Postpone the sign test until now; handle zero in the branch.
-        if (($n & 7) != 1 | $n <= 0) {
-            return $n === 0;
-        }
-        // Do it in the classical way.
-        // The correctness is not trivial as the conversion from long to double is lossy!
-        $tst = (int) sqrt($n);
-
-        return $tst * $tst === $n;
+        return abs(((int) sqrt($n)) * ((int) sqrt($n)) - $n) < 0.001;
     }
 
     /**
diff --git a/Math/Number/Prime.php b/Math/Number/Prime.php
index e791ad9d4..7076885d5 100644
--- a/Math/Number/Prime.php
+++ b/Math/Number/Prime.php
@@ -158,7 +158,7 @@ class Prime
      * @since  1.0.0
      * @author Dennis Eichhorn
      */
-    public function isPrime(int $n) : bool
+    public static function isPrime(int $n) : bool
     {
         $i = 2;
 
diff --git a/Math/Shape/D2/D2ShapeInterface.php b/Math/Shape/D2/D2ShapeInterface.php
index 93c8f2a75..e3a54ef29 100644
--- a/Math/Shape/D2/D2ShapeInterface.php
+++ b/Math/Shape/D2/D2ShapeInterface.php
@@ -30,5 +30,4 @@ use phpOMS\Math\Shape\ShapeInterface;
  */
 interface D2ShapeInterface extends ShapeInterface
 {
-    public static function getPerimeter() : float;
 }
diff --git a/Math/Shape/D3/Cone.php b/Math/Shape/D3/Cone.php
index bd8ddb98a..52ec7800c 100644
--- a/Math/Shape/D3/Cone.php
+++ b/Math/Shape/D3/Cone.php
@@ -88,8 +88,8 @@ class Cone implements D3ShapeInterface
      * @since  1.0.0
      * @author Dennis Eichhorn <d.eichhorn@oms.com>
      */
-    public static function getHeight(float $V, float $r) : float
+    public static function getHeightFromVolume(float $V, float $r) : float
     {
-        return 4 * $V / (pi() * $r ** 2);
+        return 3 * $V / (pi() * $r ** 2);
     }
 }
diff --git a/Math/Shape/D3/D3ShapeInterface.php b/Math/Shape/D3/D3ShapeInterface.php
index 9686f68c8..fb2401a53 100644
--- a/Math/Shape/D3/D3ShapeInterface.php
+++ b/Math/Shape/D3/D3ShapeInterface.php
@@ -28,7 +28,6 @@ use phpOMS\Math\Shape\ShapeInterface;
  * @link       http://orange-management.com
  * @since      1.0.0
  */
-interface D2ShapeInterface extends ShapeInterface
+interface D3ShapeInterface extends ShapeInterface
 {
-    public static function getVolume() : float;
 }
diff --git a/Math/Shape/ShapeInterface.php b/Math/Shape/ShapeInterface.php
index 3618dfec8..bc957edb1 100644
--- a/Math/Shape/ShapeInterface.php
+++ b/Math/Shape/ShapeInterface.php
@@ -28,5 +28,4 @@ namespace phpOMS\Math\Shape;
  */
 interface ShapeInterface
 {
-    public static function getSurface() : float;
 }
diff --git a/Utils/Compression/LZW.php b/Utils/Compression/LZW.php
index f5672ded7..62804fee2 100644
--- a/Utils/Compression/LZW.php
+++ b/Utils/Compression/LZW.php
@@ -81,8 +81,8 @@ class LZW implements CompressionInterface
 
         $w      = chr($compressed[0]);
         $result = $w;
-
         $count = count($compressed);
+        
         for ($i = 1; $i < $count; $i++) {
             $k = $compressed[$i];
 
@@ -97,7 +97,7 @@ class LZW implements CompressionInterface
             }
 
             $result .= $entry;
-            $dictionary[$dictSize++] = $w + $entry[0];
+            $dictionary[$dictSize++] = $w . $entry[0];
             $w                       = $entry;
         }