translation.en: 'Theme and variations' is one of those forms that require a certain kind of intellectual activity, because you are always comparing the variation with the theme that you hold in your mind.
translation.zh: 主题和变体是一种 需要特定智力活动参与的形式。 因为你总是在把变体和 已经存在于你脑海中的主题作比较。