Source: wikibot/nielsen-realization-problem
= Nielsen realization problem
{wiki=Nielsen_realization_problem}
The Nielsen realization problem is a concept in the field of algebraic topology and group theory, specifically concerning the study of free groups and their automorphisms. More formally, it deals with the conditions under which a given group presentation can be realized as the fundamental group of a topological space, usually a certain type of surface or manifold.