GENERAL CANCELLATION OF LADDER GRAPHS AT FINITE-TEMPERATURE

some cases, an important example being at finite temperature, extreme infrared, collinear, or light-cone behavior may cause the usual loop-e xpansion to break down. For some of these cases higher order ladder gr aphs can become important. In all earlier paper it was shown that, giv en a particular relation between a vertex and a self-energy function, the resummation of the ladder graphs simplifies significantly when oth er types of graphs are included in a consistent effective expansion. I n this paper we show that this assumed relation is valid for a large c lass of vertex and self-energy functions-at finite temperature.