2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/77884We give formulae for a module presentation of the module of identities among relations for a presentation of a group, in terms of information on 0- and 1-combings of the Cayley graph. This is seen as a special case of extending a partial free crossed resolution of a group given a partial contracting homotopy of its universal cover.34 pages, LaTeX2E, with xypicGroup TheoryAlgebraic Topology20F05,20J05,20L10,18G50,57M07text