irreducible 3-manifold

Improves the theorem “A finite poset is dismantlable if and only if it is dismantlable by irreducibles”, obtains a new theorem “A finite poset is homotopic dismantlable if and only if it is dismantlable by star irreducibles” and proves the equivalence of these theorems.

就Ｆｉｘｅｄ Ｐｏｉｎｔ ｉｎ Ｐｏｓｅｔ中的定理“有限偏序集Ｐ是可拆的充要條件為Ｐ是不可約可拆”進行了改進，得到了Ｐ是同倫可拆的充要條件為Ｐ是星形不可約可拆，并且證明了這兩個充要條件等價，極大地簡化了不可約可拆的判別