2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/58098Two coalgebra structures are used in quantum field theory. The first one is the coalgebra part of a Hopf algebra leading to deformation quantization. The second one is a co-module co-algebra over the first Hopf algebra and it is used to define connected chronological products and renormalization.3 pages. Paper written for the Encyclopaedia of MathematicsMathematical Physicstext