diff --git a/Classes/PHPExcel/Calculation.php b/Classes/PHPExcel/Calculation.php
index 7887a4a..1b01016 100644
--- a/Classes/PHPExcel/Calculation.php
+++ b/Classes/PHPExcel/Calculation.php
@@ -3641,21 +3641,19 @@ class PHPExcel_Calculation {
 		$this->_debugLog->writeDebugLog('Evaluation Result is ', $this->_showTypeDetails($result));
 		//	And push the result onto the stack
 		$stack->push('Value',$result);
-		return TRUE;
-	}	//	function _executeBinaryComparisonOperation()
+		return true;
+	}
 
 	/**
 	 * Compare two strings in the same way as strcmp() except that lowercase come before uppercase letters
-	 * @param string $str1
-	 * @param string $str2
-	 * @return integer
+	 * @param    string    $str1    First string value for the comparison
+	 * @param    string    $str2    Second string value for the comparison
+	 * @return   integer
 	 */
 	private function strcmpLowercaseFirst($str1, $str2)
 	{
-		$from = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz';
-		$to = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
-		$inversedStr1 = strtr($str1, $from, $to);
-		$inversedStr2 = strtr($str2, $from, $to);
+        $inversedStr1 = PHPExcel_Shared_String::StrCaseReverse($str1);
+        $inversedStr2 = PHPExcel_Shared_String::StrCaseReverse($str2);
 
 		return strcmp($inversedStr1, $inversedStr2);
 	}
diff --git a/Classes/PHPExcel/Shared/String.php b/Classes/PHPExcel/Shared/String.php
index 4921dc9..7d6b419 100644
--- a/Classes/PHPExcel/Shared/String.php
+++ b/Classes/PHPExcel/Shared/String.php
@@ -626,6 +626,41 @@ class PHPExcel_Shared_String
 		return ucwords($pValue);
 	}
 
+    public static function mb_is_upper($char)
+    {
+        return mb_strtolower($char, "UTF-8") != $char;
+    }
+
+    public static function mb_str_split($string)
+    {
+        # Split at all position not after the start: ^
+        # and not before the end: $
+        return preg_split('/(?<!^)(?!$)/u', $string );
+    }
+
+	/**
+	 * Reverse the case of a string, so that all uppercase characters become lowercase
+     *    and all lowercase characters become uppercase
+	 *
+	 * @param string $pValue UTF-8 encoded string
+	 * @return string
+	 */
+	public static function StrCaseReverse($pValue = '')
+	{
+        if (self::getIsMbstringEnabled()) {
+            $characters = self::mb_str_split($pValue);
+            foreach($characters as &$character) {
+                if(self::mb_is_upper($character)) {
+                    $character = mb_strtolower($character, 'UTF-8');
+                } else {
+                    $character = mb_strtoupper($character, 'UTF-8');
+                }
+            }
+            return implode('', $characters);
+		}
+		return strtolower($pValue) ^ strtoupper($pValue) ^ $pValue;
+	}
+
 	/**
 	 * Identify whether a string contains a fractional numeric value,
 	 *    and convert it to a numeric if it is
@@ -771,6 +806,6 @@ class PHPExcel_Shared_String
 		if (is_numeric($value))
 			return $value;
 		$v = floatval($value);
-		return (is_numeric(substr($value,0,strlen($v)))) ? $v : $value;
+		return (is_numeric(substr($value, 0, strlen($v)))) ? $v : $value;
 	}
 }
diff --git a/Classes/PHPExcel/Worksheet/AutoFilter/Column/Rule.php b/Classes/PHPExcel/Worksheet/AutoFilter/Column/Rule.php
index 4a14d7d..e602646 100644
--- a/Classes/PHPExcel/Worksheet/AutoFilter/Column/Rule.php
+++ b/Classes/PHPExcel/Worksheet/AutoFilter/Column/Rule.php
@@ -257,7 +257,7 @@ class PHPExcel_Worksheet_AutoFilter_Column_Rule
 	 *
 	 * @var string
 	 */
-	private $_operator = '';
+	private $_operator = self::AUTOFILTER_COLUMN_RULE_EQUAL;
 
 	/**
 	 * DateTimeGrouping Group Value