對於區間函數的映射，若給予某些週期軌跡的類型，是否一定會有其他週期軌跡的類型呢﹖這就是蠻有趣的強迫問題，但仍沒有簡單的答案。在這篇論文中我們考慮三種不同週期軌跡的類型，而得到在這些週期軌跡上的一些強迫關係。另一方面，我們則使用符號表示法，去計算它們線性化函數的週期點個數，而得到在數論上一些有趣的新等式。

For interval maps, given the existence of some specified "types" of periodic
orbits, must they also have some other "types" of periodic orbits? This so-called
"forcing problem" is interesting, and yet has no easy answer. In this paper, we con-
sider three different "types" of periodic orbits and obtain some forcing relations on
these periodic orbits. On the other hand, we use the method of symbolic representa-
tion to compute the number of periodic points of all periods for the linearizations of
these periodic orbits and obtain some interesting new congruence identities in number