We introduce several classes of localizations (idempotent monads) on the category of groups and study their properties and relations. The most interesting class for us is the class of localizations which coincide with their zero derived functors. We call them right exact (in the sense of Keune). We prove that a right exact localization L preserves the class of nilpotent groups and that for a finite p-group G the map G → LG is an epimorphism. We also prove that some examples of localizations (Baumslag’s P-localization with respect to a set of primes P, Bousfield’s H R-localization, Levine’s localization, Levine-Cha’s ℤ-localization) are right exact. At the end of the paper we discuss a conjecture of Farjoun about Nikolov-Segal maps and prove a very special case of this conjecture.

我们在群体类别上介绍了几类本地化（幂等单子），并研究了它们的性质和关系。对于我们而言，最有趣的类是与其零派生函子一致的本地化类。我们称它们为正确的（在Keune的意义上）。我们证明了正确的精确定位L保留了幂等群的类别，并且对于有限的p-群G，映射G→LG是一种同质。我们还证明了一些本地化的示例（关于一组素数P，鲍斯菲尔德的HR的Baumslag的P-本地化-localization，Levine的本地化，Levine-Cha的ℤ-localization）是正确的。在本文的最后，我们讨论了有关Nikolov-Segal地图的Farjoun猜想，并证明了这种猜想的一个非常特殊的情况。