ここ、なんか日本語がおかしいね 英文読む方が良いね（＾＾ https://en.wikipedia.org/wiki/%C3%89tale_cohomology 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)
