2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/185469A combinatorial formula of G.-C. Rota and J.A. Stein is taken to perform Wick re-ordering in quantum field theory. Wick's theorem becomes a Hopf algebraic identity called Cliffordization. The combinatorial method relying on Hopf algebras is highly efficient in computations and yields closed algebraic expressions. AMS Subject Classifications 2000: 81R50; 16W3014 pages, 3 FiguresHigh Energy Physics - Theorytext