Amazingly, this is also about the pigeonhole principle! 令人惊奇的是，这同样是鸽子洞原理的运用！
The initial exploration on teaching the principle of pigeonhole 抽屉原则教学初探
The pigeonhole principle is a important principle in combinatorics. 鸽巢原理是组合学中一个非常重要得原理。
The pigeonhole principle is a powerful tool used in combinatorial math. 鸽子洞原理是分析数学组合得有力工具。
This paper describes three questions; that is, the mapping background of pigeonhole principle by using the corresponding relation between different sets. 利用集合间的对应关系阐述了鸽笼原理的映射背景。