n.同义反复，赘述

原形：tautology复数：tautologies

All bachelors are unmarried men.
所有的单身汉都是未婚男子。
If it rains, the streets will be wet; if it doesn't rain, the streets won't be affected by rain.
如果下雨，街道将会是湿的；如果不下雨，街道就不会被雨水打湿。
A statement is true if and only if it is correct.
一个陈述如果并且只有当它是正确的时才是真的。
An even number is always divisible by two.
偶数总是能被二整除。
The grass is green, or the sky is blue, or both.
草是绿色的，或者天空是蓝色的，或者是两者皆然。
All squares are rectangles but not all rectangles are squares.
所有正方形都是长方形，但并非所有长方形都是正方形。
If a coin is heads, it's not tails; if it's tails, it's not heads.
如果硬币正面朝上，则背面不会朝上；如果背面朝上，则正面不会朝上。
A necessary condition for being alive is to be breathing.
活着的必要条件是要在呼吸。
Only students who have completed their studies can graduate.
只有完成学业的学生才能毕业。
The only way to win this game is to score more points than your opponent.
赢得这场比赛的唯一方法就是比对手得分多。