392 
(IT.9) 
PONTIFICIAE ACADEMIAE SCIENTIARVM SCRIPTA VARIA - 28 
21, 
x | 
x, 
don 
a, 
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Ün—1,n 
Ann 
Kaa 
Xi 
a 
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Ay) Ang + <= Unn—1 Anky Cyn, 
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A 0 
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0 
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A few words may be added about the replacement coeffi- 
cients. Each Ai (¢t=1, 2, ..., n—1I) represents the amount 
of capital, in physical terms, which is required in each period 
of time in order to keep productive capacity intact. This is the 
general definition of the a; /'s. However, it may be useful to 
adopt a simplification, because of its immediately apparent 
meaning. We may assume that in each period of time and in 
each sector, a constant proportion of the productive ca- 
pacity vanishes owing to wear and tear, so that T;=1/a; 
‘4=1, 2, ... n— I) represents a quantity which is very near 
‘though, depending on the rate of growth of the sector, not 
exactly coincidental with) the average life-time of physical 
capital goods in sector :. 
By now following exactly the same steps as in section 2, 
the condition that must be satisfied in order that the system 
may have non-trivial solutions emerges as 
I 
11.10) > Api iy + > Fan; Ain + > App; Crm = 4 
[10] Pasinetti - pag. 22