Al. I Armii W.P. 11 m. 26 
Warsaw, 20 Febr. 196? 
Dear Steindl, 
Thank you for your letter which crossed mine sent through 
Sachs. Since is the increment of T during the year 
a! r 
considered it does not differ much from , where Ai_ 
is the increment over the period . In fact all the 
argument on investment decisions could be developed for a small 
period At rather than for a year and. then in all the 
equations would be replaced by 
T 
Thus I resorted to A.J_ over an annual period only for the 
sake of simplicity / as in my preceding paper Si Observations on the 
Theory.of Growth” in Economic Journal /. I do not think that this 
simplification interferes with the generation of the cycle. 
My present theory of investment decisions differs nevertheless 
substantially from the previous one for different reasons. I 
assume now a much more definite pattern of the behaviour of the 
entrepreneur which permits to s#how that a. a 1 .1 conduct the 
argument only in terms of gross saving and gross investment and 
I introduce explicitly the influence of the increase of producti 
vity due to technical progress rather than using from the outset 
the concept of depreciation and net investment /sections 4 and 5/. 
Finally I explain the additional effect of innovations which is 
based on a sort of ’’doublecounting” by the entrepreneurs /section 
6/. The latter is important because it clarifies the problem 
raised by Mrs Robinson that all the effects of innovations are 
accounted for by depreciation. 
; ,achs told me that you are quite well but that sfpu do not