2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/23183Hedin's equations are solved perturbatively in zero dimension to count Feynman graphs for self-energy, polarization, propagator, effective potential and vertex function in a many-body theory of fermions with two-body interaction. Counting numbers are also obtained in the GW approximation.Revised published version, 3 pages, no figuresStrongly Correlated ElectronsNuclear Theorytext