invariant: Invariant[Fetch[M,?]]): Fetch[M,T] =
FT Professional
，这一点在PDF资料中也有详细论述
田轩想到一个身边人常会提及的场景：深夜做功课的孩子手指不自觉地在手机屏幕上滑动。“屏幕那头，是同学们分享的短视频，聊不完的消息，而屏幕这头，是孩子们难以自控的注意力。”
In its defence filed at the High Court in October, the BBC said it denied that he "has suffered any distress or harassment" as a result of its responses to his requests.