19/04/20 08:22:44.13 E/H8FvM1.net
>>699
>エタール・コホモロジーは係数がZ/nZの場合には上手く働くが、ねじれを持たない(たとえば整係数や有理係数)場合は満足する結果を与えない。
>エタール・コホモロジーからねじれを持たないコホモロジー群を得るためには、ねじれを持つ係数のエタール・コホモロジーの逆極限をとればよい。
ここ、なんか日本語がおかしいね
英文読む方が良いね（＾＾
URLﾘﾝｸ(en.wikipedia.org)
Etale cohomology
(抜粋)
ｌ-adic cohomology groups
In applications to algebraic geometry over a finite field Fq with characteristic p, the main objective was to find a replacement for the singular cohomology groups with integer (or rational) coefficients,
which are not available in the same way as for geometry of an algebraic variety over the complex number field. Etale cohomology works fine for coefficients Z/nZ for n co-prime to p, but gives unsatisfactory results for non-torsion coefficients.
To get cohomology groups without torsion from etale cohomology one has to take an inverse limit of etale cohomology groups with certain torsion coefficients; this is called ｌ-adic cohomology, where ｌ stands for any prime number different from p.
(引用終り)