2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/219576The key to membrane theory is to enlarge the diffeomorphism group until 4D gravity becomes almost topological. Just one ghost survives and its central charges can cancel against matter. A simple bosonic membrane emerges, but its flat D = 28 target space is unstable. Adding supersymmetry ought to give calculable (2,2) membranes in 12 target dimensions, but (2,1) membranes won't work.11 pages. Section 5 changed: some confusion corrected and explanations addedHigh Energy Physics - Theorytext