2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/147735The formalism of Ashtekar and Magnon \cite{AshtekarMagnon:1975} for the definition of particles in quantum field theory in curved spacetime is further developed. The relation between basic objects of this formalism (e.g., the complex structure) and different Green functions is found. It allows one to derive composition laws for Green functions. The relation of two definitions of particles is reformulated in the formalism and the base-independent Bogoljubov transformation is expressed using quantities which are derivable directly from the ``in-out'' Green function.28 pages; LaTeX2e document; it uses amsmath.sty, amsfonts.sty, amssymb.sty, cite.sty and ifthen.sty packages; There exists a broader version of this paper with additional review material available from http://fermi.phys.ualberta.ca/~krtous/Physics/pigf/pigf.html or by e-mail from the AuthorGeneral Relativity and Quantum Cosmologytext