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

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

l(X):=min⁡C(−KX⋅C),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 m≥lm\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.

References

Primary source

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

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