一类Mori纤维化的极面收缩态射

On contraction of extremal face which is Mori fibration

设X是n维非奇异射影簇,L是X上的丰富线丛,KX是X的典范丛,f:X→Y是极面收缩态射,其支撑除子为KX+(n-4)L.如果X与Y不是双有理等价的,那么(X,L)是一类特殊的代数簇.文中给出了(X,L)的结构的完整分类.

Let X be a nonsingular variety of dimension n, L be an ample line bundle over X and Kx be the canonical line bundle over X. Let f： X→Y be a contraction morphism of extremal face from X to Y with supporting divisor Kx ＋ （ n - 4 ） L. Suppose that X is not birational equivalent to Y, then （ X, L） must be a class of special varieties. The complete classification of （X,L） is obtained.