Schreier refinement theorem
= Schreier refinement theorem
{wiki=Schreier_refinement_theorem}
The Schreier refinement theorem is a result in group theory that deals with the relationship between subgroups and normal series of a group. It provides criteria for refining a normal series of groups, allowing for more structured decompositions of groups into simpler components. The theorem is primarily used in the study of group extensions and solvable groups.