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。
Consider our voting example from Section 1.2: three candidates A, B, and C are running for office. We decided that A …
甲和乙赢面一样大,丙只有他俩一半——然后甲退选了。按比例把甲的票重新分给乙和丙,答案干净得 2/3 和 1/3。