762 PONTIFICIAE ACADEMIAE SCIENTIARVM SCRIPTA VARIA - 28 
A process of this type can be labelled a « quasi stationary 
process ». It is characterised by the invariance of the rates p 
and i and of the characteristic functions © and 9. 
The fact that 7 and p are constant and the functions © and 9 
variant enable the formulas obtained for the case of a quasi- 
stationary process with variable growth rates to be still further 
simplified. 
Characteristic Functions 
I31. From the relation (112-2) and the fact that 9 is inva- 
riant, we deduce that 
(131-1) 
d6 
— —0O 
74 
i.e. the production period ® is constant. 
Further, from (111-6) we have 
(131-2) 
©(8)R,({)=R, (#)e(0)6°° 
and this enables the two conditions below to be deduced from 
relations (111-3) and (111-4) 
(131-3) 
(I3I-4) 
R;(t)=R._(£)) 2°00) do 
R (t;=R_1 
[Te 8 
© (e)de 
[11] Allais - pag. 66