鸽笼原理,又称抽屉原则或重叠原则,它虽然原理简单,但是如果灵活运用这一原则,可以很顺利地解决一些看上去相当复杂甚至觉得简直无从下手的数学问题.因此,常被一些国内外数学竞赛作为命题的内容之一,它不失为中学生开展课外活动的好材料. The principle of pigeonhole cage, also known as drawer principle or overlapping principle, is simple in principle, but if you use this principle flexibly, you can successfully solve some mathematical problems that seem quite complicated or even impossible to start. Therefore, it is often used by some domestic countries. The Outer Mathematics Competition is one of the contents of the proposition. It is a good material for secondary students to carry out extracurricular activities.