diff --git a/lib/MathParser/Math.php b/lib/MathParser/Math.php
index 30c67f4..3d12899 100644
--- a/lib/MathParser/Math.php
+++ b/lib/MathParser/Math.php
@@ -96,6 +96,22 @@ public function run(array $stack)
         return $operator ? $operator->render() : $this->render($stack);
     }
     
+    public function getDistinctVariables(array $stack)
+    {
+        $variables = [];
+    
+        foreach ($stack as $expression) {
+            if ($expression instanceof Variable) {
+                $variableName = $expression->getName();
+                if (!in_array($variableName, $variables, true)) {
+                    $variables[] = $variableName;
+                }
+            }
+        }
+        
+        return $variables;
+    }
+    
     private function render(array &$stack)
     {
         $output = '';
diff --git a/lib/MathParser/Variable.php b/lib/MathParser/Variable.php
index 9064439..4e05c2b 100644
--- a/lib/MathParser/Variable.php
+++ b/lib/MathParser/Variable.php
@@ -14,6 +14,11 @@ public function render($variables = [])
         }
     }
     
+    public function getName()
+    {
+        return $this->value;
+    }
+    
     public function isVariable()
     {
         return true;
diff --git a/test/MathParserTest.php b/test/MathParserTest.php
index 11e113f..a0f5de2 100644
--- a/test/MathParserTest.php
+++ b/test/MathParserTest.php
@@ -103,6 +103,7 @@ public static function provideVariableData()
             [['$0 + $2', [0, 41, 13]], 13],
             [['$a + $b', ['a' => 0, 'b' => 41, 13]], 41],
             [['$a + $b + $0', ['a' => 0, 'b' => 41, 0 => 13]], 54],
+            [['$a1 + $b2 + $0', ['a1' => 0, 'b2' => 41, 0 => 13]], 54],
             [['$0 + $2', [0, 41, 13]], 13],
             [['$0 + $2', [0, 41, 13]], 13],
         ];
@@ -110,6 +111,26 @@ public static function provideVariableData()
         return $data;
     }
     
+    /**
+     * @return mixed[][]
+     */
+    public static function provideVariableDataWithUsedVars()
+    {
+        $data = [
+            [['$0', [1]], ['0']],
+            [['$0 + $0', [1]], ['0']],
+            [['$0 + $1', [1, 41]], ['0', '1']],
+            [['$0 + $2', [0, 41, 13]], ['0', '2']],
+            [['$a + $b', ['a' => 0, 'b' => 41, 13]], ['a', 'b']],
+            [['$a + $b + $0', ['a' => 0, 'b' => 41, 0 => 13]], ['a', 'b', '0']],
+            [['$a1 + $b2 + $0', ['a1' => 0, 'b2' => 41, 0 => 13]], ['a1', 'b2', '0']],
+            [['$0 + $2', [0, 41, 13]], ['0', '2']],
+            [['10', []], []],
+        ];
+        
+        return $data;
+    }
+    
     /**
      * @return mixed[][]
      */
@@ -194,4 +215,15 @@ public function testInvalidVariableWithRegister($input, $expected)
         $mathParser->registerVariable(0, $input[1][0]);
         $mathParser->evaluate($input[0]);
     }
+    
+    /**
+     * @dataProvider provideVariableDataWithUsedVars
+     */
+    public function testDistinctVariables($input, $expected)
+    {
+        $mathParser = new Math();
+        $stack = $mathParser->parse($input[0]);
+        $vars = $mathParser->getDistinctVariables($stack);
+        $this->assertSame($expected, $vars);
+    }
 }
\ No newline at end of file