ACC for lengths of extremal rays of log canonical Fano varieties with Picard number one

Let XX be an nn-dimensional Q\mathbb Q-factorial log canonical Fano variety with Picard number one, and define

l(X):=minC(KXC),l(X):=\min_C(-K_X\cdot C),

where CC is an integral curve on XX. Set

Ln:={l(X)   X is an n-dimensional Q-factorial log canonical Fano variety with Picard number one}.\mathcal L_n:=\left\{l(X)\;\ X\text{ is an }n\text{-dimensional }\mathbb Q\text{-factorial log canonical Fano variety with Picard number one}\right\}.

ACC for lengths of extremal rays. For every nn, the set Ln\mathcal L_n satisfies the ascending chain condition: if XkX_k is an nn-dimensional Q\mathbb Q-factorial log canonical Fano variety with Picard number one for every kk and

l(X1)l(X2)l(Xk),l(X_1)\leq l(X_2)\leq\cdots\leq l(X_k)\leq\cdots,

then there is a positive integer ll such that l(Xm)=l(Xl)l(X_m)=l(X_l) for every mlm\geq l.

The paper proves this assertion for nn-dimensional Q\mathbb Q-factorial toric Fano varieties with Picard number one, while the stated general ACC remains open.

Sources & referencesView supporting material

Primary source

Osamu Fujino and Yasuhiro Ishitsuka, “On the ACC for lengths of extremal rays”, arXiv:1110.2541 (2012).

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