public function rename(string $from, string $to) : Assoc
    {
        return $this->pipe(
            function (array $values) use ($from, $to) : array {
                if (isset($values[$from])) {
                    $values[$to] = $values[$from];
                    unset($values[$from]);
                }

                return $values;
            }
        );
    }