diff --git a/rules_shipping_advanced.php b/rules_shipping_advanced.php
index e32ccbc062ede2b6b18229d155e23ef70f5b608b..df476b0db79f08958a0f307ac90a4f9e59fbe02e 100644
--- a/rules_shipping_advanced.php
+++ b/rules_shipping_advanced.php
@@ -104,24 +104,6 @@ class plgVmShipmentRules_Shipping_Advanced extends plgVmShipmentRules_Shipping_B
 /** Extend the shipping rules by allowing arbitrary mathematical expressions
  */
 class ShippingRule_Advanced extends ShippingRule {
-	var $operators = array(
-		".-" => 100, ".+" => 100,
-		" in " => 80,
-		"^"  => 70, 
-		"*"  => 60, "/"  => 60, "%"  => 60, 
-		"+"  => 50, "-"  => 50, 
-		"<"  => 40, "<=" => 40, ">"  => 40, ">=" => 40, "=>" => 40, "=<" => 40,
-		"==" => 40, "!=" => 40, "<>" => 40, "~" => 40,
-		"&&"  => 21, " AND " => 21, "AND" => 21,
-		" OR "  => 20, "OR" => 20,
-		"="  => 10,
-		
-		"("  =>  0, ")"  =>0 
-	);
-	var $unary_ops = array(
-		"-" => ".-", "+" => ".+"
-	);
-
 	function __construct ($rule, $countries, $tax_id) {
 		parent::__construct ($rule, $countries, $tax_id);
 	}
@@ -188,6 +170,21 @@ class ShippingRule_Advanced extends ShippingRule {
 		// Split at all operators:
 		$atoms = $this->tokenize_expression ($rulepart);
 		
+		$operators = array(
+			".-" => 100, ".+" => 100,
+			"in" => 80, 
+			"^"  => 70, 
+			"*"  => 60, "/"  => 60, "%"  => 60, 
+			"+"  => 50, "-"  => 50, 
+			"<"  => 40, "<=" => 40, ">"  => 40, ">=" => 40, "=>" => 40, "=<" => 40,
+			"==" => 40, "!=" => 40, "<>" => 40, "~" => 40,
+			"&&"  => 21, "AND" => 21, 
+			"OR"  => 20, 
+			"="  => 10,
+			"("  =>  0, ")"  =>0 
+		);
+		$unary_ops = array("-" => ".-", "+" => ".+");
+
 		// Any of these indicate a comparison and thus a condition:
 		$condition_ops = array('<', '<=', '=<', '<>', '!=', '==', '>', '>=', '=>', '~', ' OR ', 'OR', 'AND', ' AND ', '&&', 'in', ' in ');
 		$comparison_ops = array('<', '<=', '=<', '<>', '!=', '==', '>', '>=', '=>', '~');
@@ -266,16 +263,16 @@ class ShippingRule_Advanced extends ShippingRule {
 				} while (true);
 				$prev_token_operator = false;
 				
-			} elseif (isset($this->unary_ops[$a]) && $prev_token_operator) { // 4) UNARY operators
+			} elseif (isset($unary_ops[$a]) && $prev_token_operator) { // 4) UNARY operators
 				// Unary and binary operators need to be handled differently: 
 				// Unary operators must only pop other unary operators, never any binary operator
-				$unary_op = $this->unary_ops[$a];
+				$unary_op = $unary_ops[$a];
 				// For unary operators, pop other unary operators from the stack until you reach an opening parenthesis, 
 				// an operator of lower precedence, or a right associative symbol of equal precedence. 
 				while (count($stack)>0) { // 4a)
 					$op = array_pop ($stack);
 					// Remove all other unary operators:
-					if (in_array ($op, $this->unary_ops)) {
+					if (in_array ($op, $unary_ops)) {
 						array_push ($out_stack, $op);
 					} else {
 						// No unary operator -> add it back to stack, exit loop
@@ -286,8 +283,8 @@ class ShippingRule_Advanced extends ShippingRule {
 				array_push ($stack, $unary_op); // 4b)
 				$prev_token_operator = true;
 				
-			} elseif (isset($this->operators[$a])) { // 4) BINARY operators
-				$prec = $this->operators[$a];
+			} elseif (isset($operators[$a])) { // 4) BINARY operators
+				$prec = $operators[$a];
 				$is_condition |= in_array($a, $condition_ops);
 				$is_assignment |= ($a == "=");
 				
@@ -300,7 +297,7 @@ class ShippingRule_Advanced extends ShippingRule {
 						// add it back to the stack!
 						array_push ($stack, $op);
 						break;
-					} elseif ($this->operators[$op]<$prec) {
+					} elseif ($operators[$op]<$prec) {
 						// We found an operator with lower precedence, add it back to the stack!
 						array_push ($stack, $op); // 4b)
 						break;
@@ -356,7 +353,7 @@ class ShippingRule_Advanced extends ShippingRule {
 				array_unshift($args, $function);
 				array_unshift($args, "FUNCTION"); 
 				$stack[] = $args;
-			} elseif (in_array($e, $this->unary_ops)) { // 4) unary operators
+			} elseif (in_array($e, $unary_ops)) { // 4) unary operators
 				// Operator => apply to the last value on the stack
 				if (count($stack)<1) { // 4d)
 					JFactory::getApplication()->enqueueMessage(JText::sprintf('VMSHIPMENT_RULES_EVALUATE_SYNTAXERROR', $rulepart), 'error');
@@ -368,7 +365,7 @@ class ShippingRule_Advanced extends ShippingRule {
 				// insert the arguments to the existing comparison instead of creating a new one
 				$op = array ($e, $o1); // 4b)
 				array_push ($stack, $op); // 4c)
-			} elseif (isset($this->operators[$e])) { // 4) binary operators
+			} elseif (isset($operators[$e])) { // 4) binary operators
 				// Operator => apply to the last two values on the stack
 				if (count($stack)<2) { // 4d)
 					JFactory::getApplication()->enqueueMessage(JText::sprintf('VMSHIPMENT_RULES_EVALUATE_SYNTAXERROR', $rulepart), 'error');