## Advanced Studies in Pure Mathematics

- Adv. Stud. Pure Math.
- Algebraic Varieties and Analytic Varieties, S. Iitaka, ed. (Tokyo: Mathematical Society of Japan, 1983), 131 - 180

### Minimal Models of Canonical 3-Folds

#### Abstract

This paper introduces a temporary definition of *minimal models* of 3-folds (0.7), and studies these under extra hypotheses. The main result is Theorem (0.6), in which I characterise the singularities which necessarily appear on a minimal model, and prove the existence of a minimal model $S$ of a 3-fold of f.g. general type, by blowing up the canonical model $X$ studied in [C3-f], imitating closely the minimal resolution of Du Val surface singularities.

Apart from techniques familiar from [C3-f] (computations of the valuations of differentials; cyclic covers; crepant blow-ups of index 1 points which are not cDV), the main new element (Theorem (2.6)) is a method of blowing up the 1-dimensional singular locus, based on the Brieskorn–Tyurina result on the existence of simultaneous resolutions of a family of Du Val surface singularities, together with the elementary transformations in $(-2)$-curves of Burns and Rapoport. Part II is devoted to an exposition of these elementary transformations; much of this is folklore material, but it seems worthwhile to give a detailed account of what seems to be a key phenomenon of higher-dimensional birational geometry.

The canonical and terminal singularities introduced in [C3-f] and here have strong inductive properties, and there is some reason for believing that terminal singularities will provide the natural category for an inductive extension of Mori’s results: elementary contractions (when these exist) specified by extremal faces of the $K<0$ part of the Mori cone are always discrepant. I have included in §4 conjectures as to what the theory of minimal models and classification of 3-folds will look like in 3 or 4 years’ time, and a section of conjectures in §8 attempting to pin down the non-uniqueness of minimal models in the non-ruled case.

#### Article information

**Source***Algebraic Varieties and Analytic Varieties*, S. Iitaka, ed. (Tokyo: Mathematical Society of Japan, 1983), 131-180

**Dates**

Received: 30 September 1981

First available in Project Euclid:
24 April 2018

**Permanent link to this document**

https://projecteuclid.org/
euclid.aspm/1524598015

**Digital Object Identifier**

doi:10.2969/aspm/00110131

**Mathematical Reviews number (MathSciNet)**

MR715649

**Zentralblatt MATH identifier**

0558.14028

#### Citation

Reid, Miles. Minimal Models of Canonical 3-Folds. Algebraic Varieties and Analytic Varieties, 131--180, Mathematical Society of Japan, Tokyo, Japan, 1983. doi:10.2969/aspm/00110131. https://projecteuclid.org/euclid.aspm/1524598015