Wish to thank TFD for its existence? Tell a colleague about us, increase a link to this page, or visit the webmaster's webpage without spending a dime enjoyable information.知乎，让每一次点击都充满意义 —— 欢迎来到知乎，发现问题背后的世界。: a forward spin offered to some ball (as in golf or billiards) by placing i