618 PONTIFICIAE ACADEMIAE SCIENTIARVM SCRIPTA VARIA - 
But, most interesting of all, this is the case to which macro- 
economic models of growth can be correctly applied. Since the 
system expands keeping its proportions constant, there is in 
fact no loss of generality in framing the analysis in macro- 
economic terms. The usual convention that the variables must 
be considered as measured in terms of a composite commodity, 
made up of a fixed « basket of goods », is in this case perfectly 
legitimate and logically unobjectionable. As all our results 
have shown, since all single coefficients remain constant through 
time, the composition or structure of the system, once specified 
at time zero, remains the same for all time. 
10| Pasinetti - pag. 45