code: public function assertGreaterThan($config, $keyGreater, $keyLower)
      {
          if (!isset($config[$keyLower])
              || !isset($config[$keyGreater])
              || $config[$keyLower] >= $config[$keyGreater]) {
              throw new ConfigurationException($keyGreater." must be greater than ".$keyLower);
          }
          return $this;
      }
docs: Assert both properties are set and 1st is greater than second
  @param array $config Array being validated
  @param string|int $keyGreater Array key with greater value
  @param string|int $keyLower Array key with lower value
  @return $this
  @throws ConfigurationException On a failed assertation