2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/57831The paper investigates relations between the phase space structure of a quantum field theory ("nuclearity") and the concept of pointlike localized fields. Given a net of local observable algebras, a phase space condition is introduced that allows a very detailed description of the theory's field content. An appendix discusses noninteracting models as examples.v3: minor changes, as to appear in J. Math. Phys.; 15 pagesMathematical Physics81T05text