5.8. Residual boundaries [0173]
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5.8. Residual boundaries
The following construction plays a crucial role for the understanding of the limit measure appearing in Corollary B.
Consider a model metric of defined on a proper dlt model . Following §3.1 we explain how to associate a subklt pair to each stratum of corresponding to a maximal simplex in .
Let us first recall a few facts about adjunction. When is an snc model, each stratum comes with a boundary . Here is log smooth, and
| (5.6) |
the identification being provided by Poincaré residues. When is merely dlt, each stratum is normal, and comes with a canonically defined effective -divisor such that is dlt and still satisfies (5.6) (cf. [Kol13, 4.19]). We have
where is an effective -divisor supported in the complement of .
Example 5.11.
For each , contains finitely many prime divisors of . At the generic point of , has cyclic quotient singularities, and
with the order of the corresponding cyclic groups, cf. [Kol13, 3.36.3].
Now let be a model metric on , determined by a model of on a proper dlt model of . Introduce as before the function on , and note that the -Cartier divisor
is effective.
Lemma 5.12.
If is a stratum of corresponding to a face of , then . It follows that the -Cartier divisor
is well-defined, and we have a canonical identification as -line bundles. Further, if is a maximal face of , then the pair is subklt.
We emphasize that is not effective in general.
Proof.
The first two points are clear. When is a maximal face, each meeting satisfies . As a result, contains each lc center of , which yields the last assertion. ∎