John C. Herzel. Green's Functions and Double‐Time Distribution Functions in Classical Statistical Mechanics. Journ. of Math. Phys. 8 (1967) 1650; DOI: http://dx.doi.org/10.1063/1.1705404. John C. Herzel. Classical Green's Functions in Response Theory. Journ. of Math. Phys. 11 (1970) 741; DOI: http://dx.doi.org/10.1063/1.1665204.