2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/229944We prove that the additive group of the rationals does not have an automatic presentation. The proof also applies to certain other abelian groups, for example, torsion-free groups that are $p$-divisible for infinitely many primes $p$, or $Q/Z$. The proof is combinatorial and uses most notably Freiman's theorem on sets with small doubling.11 pagesLogicCombinatoricstext