diff --git a/README.md b/README.md
index 98740d6..69651d5 100644
--- a/README.md
+++ b/README.md
@@ -9,6 +9,7 @@
 * Conditional If logic
 * Support for user defined operators
 * Support for user defined functions
+* Dynamic variable resolution (delayed computation)
 * Unlimited variable name lengths
 * String support, as function parameters or as evaluated as a number by PHP
 * Exceptions on divide by zero, or treat as zero
@@ -128,6 +129,21 @@ $executor->setVar('var1', 0.15)->setVar('var2', 0.22);
 
 echo $executor->execute("$var1 + $var2");
 ```
+
+You can dynamically define variables at run time. If a variable has a high computation cost, but might not be used, then you can define an undefined variable handler. It will only get called when the variable is used, rather than having to always set it initially.
+
+```php
+$calculator = new MathExecutor();
+$calculator->setVarNotFoundHandler(
+    function ($varName) {
+        if ($varName == 'trans') {
+            return transmogrify();
+        }
+        return null;
+    }
+);
+```
+
 ## Division By Zero Support:
 Division by zero throws a `\NXP\Exception\DivisionByZeroException` by default
 ```php
diff --git a/tests/MathTest.php b/tests/MathTest.php
index d76a57c..2669ccd 100644
--- a/tests/MathTest.php
+++ b/tests/MathTest.php
@@ -416,13 +416,21 @@ public function testStringComparison()
         $this->assertEquals(true, $calculator->execute('"hello world" == "hello world"'));
         $this->assertEquals(false, $calculator->execute('"hello world" == "hola mundo"'));
         $this->assertEquals(true, $calculator->execute('"hello world" != "hola mundo"'));
+        $this->assertEquals(true, $calculator->execute('"a" < "b"'));
+        $this->assertEquals(false, $calculator->execute('"a" > "b"'));
+        $this->assertEquals(true, $calculator->execute('"a" <= "b"'));
+        $this->assertEquals(false, $calculator->execute('"a" >= "b"'));
+        $this->assertEquals(true, $calculator->execute('"A" != "a"'));
     }
 
     public function testVarStringComparison()
     {
         $calculator = new MathExecutor();
-        $calculator->setVar('var', 0);
-        $this->assertEquals($calculator->execute('0 == "a"'), $calculator->execute('var == "a"'));
+        $calculator->setVar('var', 97);
+        $this->assertEquals(false, $calculator->execute('97 == "a"'));
+        $this->assertEquals(false, $calculator->execute('$var == "a"'));
+        $calculator->setVar('var', 'a');
+        $this->assertEquals(true, $calculator->execute('$var == "a"'));
     }
 
     public function testOnVarNotFound()
@@ -432,9 +440,8 @@ public function testOnVarNotFound()
             function ($varName) {
                 if ($varName == 'undefined') {
                     return 3;
-                } else {
-                    return null;
                 }
+                return null;
             }
         );
         $this->assertEquals(15, $calculator->execute('5 * undefined'));
@@ -446,4 +453,28 @@ public function testMinusZero()
         $this->assertEquals(1, $calculator->execute('1 - 0'));
         $this->assertEquals(1, $calculator->execute('1-0'));
     }
+
+    public function testGetFunctionsReturnsArray()
+    {
+        $calculator = new MathExecutor();
+        $this->assertIsArray($calculator->getFunctions());
+    }
+
+    public function testGetFunctionsReturnsFunctions()
+    {
+        $calculator = new MathExecutor();
+        $this->assertGreaterThan(40, count($calculator->getFunctions()));
+    }
+
+    public function testGetVarsReturnsArray()
+    {
+        $calculator = new MathExecutor();
+        $this->assertIsArray($calculator->getVars());
+    }
+
+    public function testGetVarsReturnsCount()
+    {
+        $calculator = new MathExecutor();
+        $this->assertGreaterThan(1, count($calculator->getVars()));
+    }
 }