SEMAINE D'ÉTUDE SUR LE ROLE DE L’ANALYSE ECONOMETRIQUE ETC. 255 
The homogeneity of the production function enables us tu 
go over to per-unit-of-labor-force concepts. Calling the unit 
of labor force briefly a « worker », let x denote consumption 
per worker, y ditto net investment, z ditto capital stock, and 
(9) 
output per worker. Since we then have 
the feasible set in the space of per-worker variables + 
romes 
(ro) (10a 
) (IOd.€ 
Ver 
The term Jz represents the (net) investment needed if one 
wants merely to supply the growing labor force with capital 
at the existing ratio of capital per worker. 
To be specific we shall call a path (x, z,) satisfying (10) 
attainable (for the given z,), and use the term feasible path ir 
the wider sense of a path attainable for some z,>o0. 
It is implied in (7 e) that f(z) is strictly concave 
{!) A strictlv concave function is one that is strictly « above » all its 
rhorde 
41 Koopmans - pag. 1)