2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/152392With the help of the complex structure and the wave operator of the nonlinear classical Klein-Gordon equation with the interaction $u^4_4$ we define the Wick kernel of the interacting quantum field in four-dimensional space-time and consider its properties. In particular, the diagonal of this Wick kernel is (real) solutions of the classical nonlinear Klein-Gordon equation with the interaction $u^4_4.$19 pages, LaTeXFunctional AnalysisHigh Energy Physics - TheoryMathematical PhysicsExactly Solvable and Integrable SystemsQuantum Physicstext