Reidemeister–Schreier Method

A constructive procedure to obtain a presentation (generators and relations) for a subgroup H of a group G given a presentation of G; using a Schreier transversal one computes Schreier generators for H and derives relations by rewriting the relators of G in terms of these generators.

A constructive procedure that, given a finitely presented group G and a chosen transversal of cosets for a subgroup H ≤ G, produces a presentation of H by rewriting the generators and relations of G relative to the transversal.