Inversion of adjunction for arbitrary-codimension subvarieties

Let XX be a nonsingular variety over a field of characteristic zero, and let Y=i=1ktiYiY=\sum_{i=1}^k t_iY_i be a formal combination where ti>0t_i>0 are real numbers and each YiXY_i\subsetneq X is a closed subscheme. Let ZXZ\subsetneq X be a normal Q\mathbb{Q}-Gorenstein closed subvariety of codimension r>0r>0 such that Z⊄i=1kYiZ\not\subset\bigcup_{i=1}^kY_i. Inversion-of-adjunction conjecture. If the pair (X,Y+rZ)(X,Y+rZ) is plt (respectively, lc) near ZZ, then the pair (Z,YZ)(Z,Y|_Z) is klt (respectively, lc). This proposes an inversion-of-adjunction principle for arbitrary codimension, extending the known local-complete-intersection case; the paper presents it as suggested by the relationship between dense F-pure type and lc pairs, and between purely F-regular type and plt pairs.

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Primary source

Shunsuke Takagi, “F-singularities of pairs and Inversion of Adjunction of arbitrary codimension”, arXiv:math/0305286 (2003).

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