## Foliations and inseparable morphisms.(English)Zbl 0659.14018

Algebraic geometry, Proc. Summer Res. Inst., Brunswick/Maine 1985, part 2, Proc. Symp. Pure Math. 46, No. 2, 139-149 (1987).
[For the entire collection see Zbl 0626.00011.]
The author proves a number of characterizations of groupoid schemes and formal equivalence relations in terms of Lie algebras in positive characteristic. He then introduces foliations as certain sheaves of differential operators on a smooth variety and relates them to groupoid schemes. These techniques are applied to obtain the following results:
(1) the Albanese map of a surface of non-positive Kodaira dimension is separable if its image is two-dimensional;
(2) a minimal surface in characteristic p is either uniruled or satisfies $$-c_ 2\cdot (p-1)^ 2\leq p\cdot c^ 2_ 1$$.
Reviewer: F.Herrlich

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### MSC:

 14G15 Finite ground fields in algebraic geometry 14B25 Local structure of morphisms in algebraic geometry: étale, flat, etc. 14L99 Algebraic groups

Zbl 0626.00011