线线/线面/面面的平行与垂直，各有一套判定定理与性质定理。
Suppose that we have a coin which comes up heads with probability p, and tails with probability q. Now suppose th…
一枚偏币，正面的概率是 p。连扔两次，第一次正面和第二次反面——这两件事到底算不算独立？
