2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/63445We re-cast in a more combinatorial and computational form the foldings approach of John Stallings and pursue a detailed study of the subgroup structure of free groups. In particular, we introduce the notions of an "algebraic" and a "free" extension for subgroups of free groups and apply these notions to obtain a number of algebraic and algorithmic results.41 pages, 10 figuresGroup Theory20Ftext