Existence of complements conjecture for log canonical pairs

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Let dd be a positive integer, let Γ⊂[0,1]\Gamma\subset[0,1] be a DCC set, and let (X/Z∋z,B)(X/Z\ni z,B) be an R\mathbb{R}-complementary pair of dimension dd whose boundary coefficients lie in Γ\Gamma. An nn-complement (X/Z∋z,B+)(X/Z\ni z,B^+) means that (X/Z∋z,B+)(X/Z\ni z,B^+) is log canonical,

nB+≥⌊(n+1){B}⌋+n⌊B⌋,nB^+\geq \lfloor(n+1)\{B\}\rfloor+n\lfloor B\rfloor,

and

n(KX+B+)∼0n(K_X+B^+)\sim 0

over a neighborhood of zz.

Existence of Complements Conjecture. There exists a positive integer nn, depending only on dd and Γ\Gamma, such that every such pair (X/Z∋z,B)(X/Z\ni z,B) has an nn-complement (X/Z∋z,B+)(X/Z\ni z,B^+). Moreover, if the closure of Γ\Gamma belongs to [0,1]∩Q[0,1]\cap\mathbb Q, then B+B^+ can be chosen so that B+≥BB^+\geq B.

Uniform complements are a key input for canonical bundle formulas and boundedness arguments. The conjecture is known in dimensions at most three, while the general case remains open.

References

Primary source

Guodu Chen, Jingjun Han and Wenfei Liu, “On the Iitaka volumes of log canonical surfaces and threefolds”, arXiv:2407.07391 (2024).

Additional references

3 papers in this index state this conjecture (2020–2024). The statement above is taken from the most recent of them; the others are arXiv:2301.04813, arXiv:2002.02246.

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