306 PONTIFICIAE ACADEMIAE SCIENTIARVM SCRIPTA VARIA - 28 
Value ot R,- R, 
In the case of the exponential model, we have, according 
to (251-4) 
(251-20) R,-R,=[r_ 2 (i-¢) | R, 
1+O,: 
oo P 0, R, 
for small values of ¢ and p. Now, from (110-6) and (251-9), 
we have 
(251-21) 
at _ e, Ra 
di di 
=0 OR 
Thus we have 
(251-22) 
dt 
(1 
Thus, in the exponential case consumed income is practically 
equal to capital income (see § 116) and we have from (116-22), 
(251-20) and (110-2) 
251-23) : R. ~ R.+iC 
(!) We have also this property in the general case. In this case. we have 
from (231-3), (123-2), (122-4), (224-2) and (220-2) 
1 
rel vy Ro Ÿ ? ® Ro 
I1—4(G—e)] 
à GS 5° Re 960 Ro 
II] Allais - pag. 110