code: public function execute(array $arguments) {
      	if (empty($arguments)) throw new \InvalidArgumentException("Subtraction: At least 1 argument is required");
      	//emulate CLISP: (- 3) = -3
      	if (!isset($arguments[1])) return -$arguments[0];
      	//obtain first argument
          $result = array_shift($arguments);
          foreach ($arguments as $value)
          	$result -= $value;
          return $result;
      }
docs: Obtains the result of subtracting the first element on a list by the rest of the elements.
  Usage: (- 120 30 50)
  Returns: number
  (non-PHPdoc)
  @see \eMacros\Runtime\GenericFunction::execute()